diff --git a/app/controllers/admin/customers_controller.rb b/app/controllers/admin/customers_controller.rb
index 4e48ac68ea..3d4f47bd07 100644
--- a/app/controllers/admin/customers_controller.rb
+++ b/app/controllers/admin/customers_controller.rb
@@ -67,7 +67,7 @@ module Admin
 
     def collection
       if json_request? && params[:enterprise_id].present?
-        CustomersWithBalance.new(managed_enterprise_id).query.
+        CustomersWithBalance.new(Customer.of(managed_enterprise_id)).query.
           includes(
             :enterprise,
             { bill_address: [:state, :country] },
diff --git a/app/controllers/api/v1/base_controller.rb b/app/controllers/api/v1/base_controller.rb
index e01fe3aab3..cc62b6978f 100644
--- a/app/controllers/api/v1/base_controller.rb
+++ b/app/controllers/api/v1/base_controller.rb
@@ -106,7 +106,9 @@ module Api
       end
 
       def json_api_error(message, **options)
-        { errors: [{ detail: message }] }.merge(options)
+        error_options = options.delete(:error_options) || {}
+
+        { errors: [{ detail: message }.merge(error_options)] }.merge(options)
       end
 
       def json_api_invalid(message, errors)
diff --git a/app/controllers/api/v1/customers_controller.rb b/app/controllers/api/v1/customers_controller.rb
index 24bd1db8ee..86bf05fc65 100644
--- a/app/controllers/api/v1/customers_controller.rb
+++ b/app/controllers/api/v1/customers_controller.rb
@@ -6,11 +6,17 @@ module Api
   module V1
     class CustomersController < Api::V1::BaseController
       include AddressTransformation
+      include ExtraFields
 
       skip_authorization_check only: :index
 
       before_action :authorize_action, only: [:show, :update, :destroy]
 
+      # Query parameters
+      before_action only: [:index] do
+        @extra_customer_fields = extra_fields :customer, [:balance]
+      end
+
       def index
         @pagy, customers = pagy(search_customers, pagy_options)
 
@@ -51,7 +57,11 @@ module Api
       private
 
       def customer
-        @customer ||= Customer.find(params[:id])
+        @customer ||= if action_name == "show"
+                        CustomersWithBalance.new(Customer.where(id: params[:id])).query.first!
+                      else
+                        Customer.find(params[:id])
+                      end
       end
 
       def authorize_action
@@ -61,6 +71,11 @@ module Api
       def search_customers
         customers = visible_customers.includes(:bill_address, :ship_address)
         customers = customers.where(enterprise_id: params[:enterprise_id]) if params[:enterprise_id]
+
+        if @extra_customer_fields.include?(:balance)
+          customers = CustomersWithBalance.new(customers).query
+        end
+
         customers.ransack(params[:q]).result.order(:id)
       end
 
diff --git a/app/controllers/concerns/extra_fields.rb b/app/controllers/concerns/extra_fields.rb
new file mode 100644
index 0000000000..058e986a13
--- /dev/null
+++ b/app/controllers/concerns/extra_fields.rb
@@ -0,0 +1,32 @@
+# frozen_string_literal: true
+
+# To be included in api controllers for handeling query params
+module ExtraFields
+  extend ActiveSupport::Concern
+
+  def invalid_query_param(name, status, msg)
+    render status: status, json: json_api_error(msg, error_options:
+      {
+        title: I18n.t("api.query_param.error.title"),
+        source: { parameter: name },
+        status: status,
+        code: Rack::Utils::SYMBOL_TO_STATUS_CODE[status]
+      })
+  end
+
+  def extra_fields(type, available_fields)
+    fields = params.dig(:extra_fields, type)&.split(',')&.compact&.map(&:to_sym)
+    return [] if fields.blank?
+
+    unknown_fields = fields - available_fields
+
+    if unknown_fields.present?
+      invalid_query_param(
+        "extra_fields[#{type}]", :unprocessable_entity,
+        I18n.t("api.query_param.error.extra_fields", fields: unknown_fields.join(', '))
+      )
+    end
+
+    fields
+  end
+end
diff --git a/app/json_schemas/customer_schema.rb b/app/json_schemas/customer_schema.rb
index ecced41793..1156ef8327 100644
--- a/app/json_schemas/customer_schema.rb
+++ b/app/json_schemas/customer_schema.rb
@@ -61,4 +61,9 @@ class CustomerSchema < JsonApiSchema
   def self.relationships
     [:enterprise]
   end
+
+  # Optional attributes included with eg: CustomerSchema.schema(extra_fields: :balance)
+  def self.balance
+    { balance: { type: :number, format: :double } }
+  end
 end
diff --git a/app/json_schemas/json_api_schema.rb b/app/json_schemas/json_api_schema.rb
index 069de6633d..53202656d0 100644
--- a/app/json_schemas/json_api_schema.rb
+++ b/app/json_schemas/json_api_schema.rb
@@ -19,84 +19,77 @@ class JsonApiSchema
     end
 
     def schema(options = {})
-      {
-        type: :object,
-        properties: {
-          data: {
-            type: :object,
-            properties: data_properties(**options)
-          },
-          meta: { type: :object },
-          links: { type: :object }
-        },
-        required: [:data]
-      }
+      Structure.schema(data_properties(**options))
     end
 
     def collection(options)
-      {
-        type: :object,
-        properties: {
-          data: {
-            type: :array,
-            items: {
-              type: :object,
-              properties: data_properties(**options)
-            }
-          },
-          meta: {
-            type: :object,
-            properties: {
-              pagination: {
-                type: :object,
-                properties: {
-                  results: { type: :integer, example: 250 },
-                  pages: { type: :integer, example: 5 },
-                  page: { type: :integer, example: 2 },
-                  per_page: { type: :integer, example: 50 },
-                }
-              }
-            },
-            required: [:pagination]
-          },
-          links: {
-            type: :object,
-            properties: {
-              self: { type: :string },
-              first: { type: :string },
-              prev: { type: :string, nullable: true },
-              next: { type: :string, nullable: true },
-              last: { type: :string }
-            }
-          }
-        },
-        required: [:data, :meta, :links]
-      }
+      Structure.collection(data_properties(**options))
     end
 
     private
 
-    def data_properties(require_all: false)
+    def data_properties(require_all: false, extra_fields: nil)
+      extra_fields_result = get_extra_fields(extra_fields)
+      attributes = get_attributes(extra_fields_result)
+      required = get_required(require_all, extra_fields, extra_fields_result)
+
+      Structure.data_properties(object_name, attributes, required, relationship_properties)
+    end
+
+    def relationship_properties
+      relationships.to_h { |name| [name, relationship_schema(name)] }
+    end
+
+    # Example
+    # MySchema.schema(extra_fields: :my_method)
+    # => extra_fields_result = MySchema.my_method
+    # => attributes = attributes.merge(extra_fields_result)
+    #
+    # MySchema.schema(extra_fields: {name: :my_method, required: true, opts: {method_opt: true}})
+    # => extra_fields_result = MySchema.my_method(method_opt: true)
+    # => attributes = attributes.merge(extra_fields_result)
+    # => required += extra_fields_result.keys
+    #
+    # MySchema.schema(extra_fields: [:my_method, :another_method])
+    # => extra_fields_result = MySchema.my_method.merge(another_method)
+    # => attributes = attribtues.merge(extra_fields_result)
+    #
+    # To test use eg:
+    # MySchema.schema(extra_fields: :my_method)
+    #   .dig(:properties, :data, :properties, :attributes)
+    def get_extra_fields(extra_fields)
+      case extra_fields
+      when Symbol
+        public_send(extra_fields)
+      when Hash
+        public_send(extra_fields[:name], **extra_fields[:opts].to_h)
+      when Array
+        obj = {}
+
+        extra_fields.each do |w|
+          obj.merge!(get_extra_fields(w))
+        end
+
+        obj
+      end
+    end
+
+    def get_required(require_all, extra_fields, extra_fields_result)
       required = require_all ? all_attributes : required_attributes
 
-      {
-        id: { type: :string, example: "1" },
-        type: { type: :string, example: object_name },
-        attributes: {
-          type: :object,
-          properties: attributes,
-          required: required
-        },
-        relationships: {
-          type: :object,
-          properties: relationships.to_h do |name|
-            [
-              name,
-              relationship_schema(name)
-            ]
-          end
-        }
-      }
+      if extra_fields.is_a?(Hash) && extra_fields[:required] == true && extra_fields_result.present?
+        required += extra_fields_result.keys
+      end
+
+      required
+    end
+
+    def get_attributes(extra_fields_result)
+      if [extra_fields_result, attributes].all?{ |obj| obj.respond_to?(:merge) }
+        attributes.merge(extra_fields_result)
+      else
+        attributes
+      end
     end
 
     def relationship_schema(name)
diff --git a/app/json_schemas/json_api_schema/structure.rb b/app/json_schemas/json_api_schema/structure.rb
new file mode 100644
index 0000000000..ea72753776
--- /dev/null
+++ b/app/json_schemas/json_api_schema/structure.rb
@@ -0,0 +1,83 @@
+# frozen_string_literal: true
+
+# rubocop:disable Metrics/MethodLength
+
+class JsonApiSchema
+  module Structure
+    extend self
+
+    def schema(data_properties)
+      {
+        type: :object,
+        properties: {
+          data: {
+            type: :object,
+            properties: data_properties
+          },
+          meta: { type: :object },
+          links: { type: :object }
+        },
+        required: [:data]
+      }
+    end
+
+    def collection(data_properties)
+      {
+        type: :object,
+        properties: {
+          data: {
+            type: :array,
+            items: {
+              type: :object,
+              properties: data_properties
+            }
+          },
+          meta: {
+            type: :object,
+            properties: {
+              pagination: {
+                type: :object,
+                properties: {
+                  results: { type: :integer, example: 250 },
+                  pages: { type: :integer, example: 5 },
+                  page: { type: :integer, example: 2 },
+                  per_page: { type: :integer, example: 50 },
+                }
+              }
+            },
+            required: [:pagination]
+          },
+          links: {
+            type: :object,
+            properties: {
+              self: { type: :string },
+              first: { type: :string },
+              prev: { type: :string, nullable: true },
+              next: { type: :string, nullable: true },
+              last: { type: :string }
+            }
+          }
+        },
+        required: [:data, :meta, :links]
+      }
+    end
+
+    def data_properties(object_name, attributes, required, relationship_properties)
+      {
+        id: { type: :string, example: "1" },
+        type: { type: :string, example: object_name },
+        attributes: {
+          type: :object,
+          properties: attributes,
+          required: required
+        },
+        relationships: {
+          type: :object,
+          properties: relationship_properties
+        }
+      }
+    end
+  end
+end
+
+# rubocop:enable Metrics/MethodLength
diff --git a/app/queries/customers_with_balance.rb b/app/queries/customers_with_balance.rb
index 4abd070d34..553ca88cec 100644
--- a/app/queries/customers_with_balance.rb
+++ b/app/queries/customers_with_balance.rb
@@ -1,28 +1,22 @@
 # frozen_string_literal: true
 
-# Fetches the customers of the specified enterprise including the aggregated balance across the
-# customer's orders. That is, we get the total balance for each customer with this enterprise.
+# Adds an aggregated 'balance_value' to each customer based on their order history
+#
 class CustomersWithBalance
-  def initialize(enterprise)
-    @enterprise = enterprise
+  def initialize(customers)
+    @customers = customers
   end
 
   def query
-    Customer.of(enterprise).
+    @customers.
       joins(left_join_complete_orders).
       group("customers.id").
       select("customers.*").
-      select(outstanding_balance_sum)
+      select("#{outstanding_balance_sum} AS balance_value")
   end
 
   private
 
-  attr_reader :enterprise
-
-  def outstanding_balance_sum
-    "SUM(#{OutstandingBalance.new.statement}) AS balance_value"
-  end
-
   # The resulting orders are in states that belong after the checkout. Only these can be considered
   # for a customer's balance.
   def left_join_complete_orders
@@ -36,4 +30,8 @@ class CustomersWithBalance
     states = Spree::Order::FINALIZED_STATES.map { |state| Arel::Nodes.build_quoted(state) }
     Arel::Nodes::In.new(Spree::Order.arel_table[:state], states)
   end
+
+  def outstanding_balance_sum
+    "SUM(#{OutstandingBalance.new.statement})::float"
+  end
 end
diff --git a/app/serializers/api/v1/customer_serializer.rb b/app/serializers/api/v1/customer_serializer.rb
index b5e59648b5..d558728d75 100644
--- a/app/serializers/api/v1/customer_serializer.rb
+++ b/app/serializers/api/v1/customer_serializer.rb
@@ -16,6 +16,10 @@ module Api
         address(object.shipping_address)
       end
 
+      attribute :balance, if: proc { |record|
+        record.respond_to?(:balance_value)
+      }, &:balance_value
+
       belongs_to :enterprise, links: {
         related: ->(object) {
           url_helpers.api_v1_enterprise_url(id: object.enterprise_id)
diff --git a/config/locales/en.yml b/config/locales/en.yml
index 18d8764c05..e2f487ad7e 100644
--- a/config/locales/en.yml
+++ b/config/locales/en.yml
@@ -1624,6 +1624,11 @@ en:
       destroy_attachment_does_not_exist: "Terms and Conditions file does not exist"
     orders:
       failed_to_update: "Failed to update order"
+    query_param:
+      error: 
+        title: Invalid query parameter
+        extra_fields: "Unsupported fields: %{fields}" 
+      
 
 # Frontend views
 #
diff --git a/spec/controllers/admin/customers_controller_spec.rb b/spec/controllers/admin/customers_controller_spec.rb
index 9630772d86..a60402f0bf 100644
--- a/spec/controllers/admin/customers_controller_spec.rb
+++ b/spec/controllers/admin/customers_controller_spec.rb
@@ -45,7 +45,7 @@ module Admin
             it 'calls CustomersWithBalance' do
               customers_with_balance = instance_double(CustomersWithBalance)
               allow(CustomersWithBalance)
-                .to receive(:new).with(enterprise) { customers_with_balance }
+                .to receive(:new).with(Customer.of(enterprise)) { customers_with_balance }
 
               expect(customers_with_balance).to receive(:query) { Customer.none }
 
diff --git a/spec/controllers/concerns/extra_fields_spec.rb b/spec/controllers/concerns/extra_fields_spec.rb
new file mode 100644
index 0000000000..463427926b
--- /dev/null
+++ b/spec/controllers/concerns/extra_fields_spec.rb
@@ -0,0 +1,60 @@
+# frozen_string_literal: true
+
+require 'spec_helper'
+
+describe ExtraFields do
+  let(:dummy_controller) { Api::V1::BaseController.new.extend ExtraFields }
+
+  describe "#invalid_query_param" do
+    it "renders error" do
+      allow(dummy_controller).to receive(:render) {}
+      dummy_controller.invalid_query_param("param", :unprocessable_entity, "error message")
+      expect(dummy_controller).to have_received(:render).with(
+        json:
+          {
+            errors:
+            [{
+              code: 422,
+              detail: "error message",
+              source: { parameter: "param" },
+              status: :unprocessable_entity,
+              title: "Invalid query parameter"
+            }]
+          },
+        status: :unprocessable_entity
+      )
+    end
+  end
+
+  describe "#extra_fields" do
+    context "when fields present and available" do
+      it "returns extra fields" do
+        allow(dummy_controller).to receive(:params).
+          and_return({ extra_fields: { customer: "balance" } })
+        expect(dummy_controller.extra_fields(:customer, [:balance])).to eq([:balance])
+      end
+    end
+
+    context "when fields missing" do
+      it "returns empty arr" do
+        allow(dummy_controller).to receive(:params).and_return({})
+        expect(dummy_controller.extra_fields(:customer, [:balance])).to eq([])
+      end
+    end
+
+    context "when fields not in available fields" do
+      it "calls invalid_query_param" do
+        allow(dummy_controller).to receive(:invalid_query_param) {}
+        allow(dummy_controller).to receive(:params).
+          and_return({ extra_fields: { customer: "unknown" } })
+        dummy_controller.extra_fields(:customer, [:balance])
+
+        expect(dummy_controller).to have_received(:invalid_query_param).with(
+          "extra_fields[customer]",
+          :unprocessable_entity,
+          "Unsupported fields: unknown"
+        )
+      end
+    end
+  end
+end
diff --git a/spec/queries/customers_with_balance_spec.rb b/spec/queries/customers_with_balance_spec.rb
index 479be6b410..9bf075367a 100644
--- a/spec/queries/customers_with_balance_spec.rb
+++ b/spec/queries/customers_with_balance_spec.rb
@@ -3,7 +3,7 @@
 require 'spec_helper'
 
 describe CustomersWithBalance do
-  subject(:customers_with_balance) { described_class.new(customer.enterprise.id) }
+  subject(:customers_with_balance) { described_class.new(Customer.where(id: customer)) }
 
   describe '#query' do
     let(:customer) { create(:customer) }
@@ -18,6 +18,23 @@ describe CustomersWithBalance do
       customers_with_balance.query
     end
 
+    describe 'arguments' do
+      context 'with customers collection' do
+        it 'returns balance' do
+          customers = create_pair(:customer)
+          query = described_class.new(Customer.where(id: customers)).query
+          expect(query.pluck(:id)).to eq([customers.first.id, customers.second.id])
+          expect(query.map(&:balance_value)).to eq([0, 0])
+        end
+      end
+
+      context 'with empty customers collection' do
+        it 'returns empty customers collection' do
+          expect(described_class.new(Customer.none).query).to eq([])
+        end
+      end
+    end
+
     context 'when orders are in cart state' do
       before do
         create(:order, customer: customer, total: order_total, payment_total: 0, state: 'cart')
diff --git a/spec/requests/api/v1/customers_spec.rb b/spec/requests/api/v1/customers_spec.rb
index 047c5e0438..3a4b7b38bb 100644
--- a/spec/requests/api/v1/customers_spec.rb
+++ b/spec/requests/api/v1/customers_spec.rb
@@ -26,10 +26,13 @@ describe "Customers", type: :request do
     get "List customers" do
       tags "Customers"
       parameter name: :enterprise_id, in: :query, type: :string
+      parameter name: "extra_fields[customer]", in: :query, type: :string, example: :balance,
+                description: "Add extra fields to each customer"
       produces "application/json"
 
       response "200", "Customers list" do
         param(:enterprise_id) { enterprise1.id }
+        param("extra_fields[customer]") { :balance }
         schema "$ref": "#/components/schemas/customers_collection"
 
         run_test!
@@ -105,6 +108,33 @@ describe "Customers", type: :request do
       end
     end
 
+    describe "query parameters" do
+      describe "extra_fields[customer]" do
+        context "with balance" do
+          it "adds balance to each customer" do
+            get "/api/v1/customers", params: { extra_fields: { customer: :balance } }
+            balances = json_response[:data].map{ |c| c[:attributes][:balance] }
+            expect(balances.all?{ |b| b.is_a? Numeric }).to eq(true)
+          end
+        end
+
+        context "with unknown field" do
+          it "returns unprocessable entity" do
+            get "/api/v1/customers", params: { extra_fields: { customer: :unknown } }
+            expect([response.status, json_error_detail]).to eq [422, "Unsupported fields: unknown"]
+          end
+        end
+
+        context "when not recevied" do
+          it "does not add balances" do
+            get "/api/v1/customers"
+            balances = json_response[:data].map{ |c| c[:attributes][:balance] }
+            expect([response.status, balances.compact]).to eq [200, []]
+          end
+        end
+      end
+    end
+
     post "Create customer" do
       tags "Customers"
       consumes "application/json"
@@ -191,7 +221,10 @@ describe "Customers", type: :request do
 
       response "200", "Customer" do
         param(:id) { customer1.id }
-        schema "$ref": "#/components/schemas/customer"
+        schema CustomerSchema.schema(
+          require_all: true,
+          extra_fields: { name: :balance, required: true }
+        )
 
         run_test! do
           date_time_string =
diff --git a/spec/swagger_helper.rb b/spec/swagger_helper.rb
index ad4cd3c34e..bebca37075 100644
--- a/spec/swagger_helper.rb
+++ b/spec/swagger_helper.rb
@@ -27,8 +27,9 @@ RSpec.configure do |config|
       components: {
         schemas: {
           error_response: ErrorsSchema.schema,
+          # only customer#show is with extra_fields: {name: :balance, required: true}
           customer: CustomerSchema.schema(require_all: true),
-          customers_collection: CustomerSchema.collection(require_all: true)
+          customers_collection: CustomerSchema.collection(require_all: true, extra_fields: :balance)
         },
         securitySchemes: {
           api_key_header: {
diff --git a/swagger/v1/swagger.yaml b/swagger/v1/swagger.yaml
index 2909306e6e..82ae1aab26 100644
--- a/swagger/v1/swagger.yaml
+++ b/swagger/v1/swagger.yaml
@@ -77,7 +77,7 @@ components:
                 billing_address:
                   type: object
                   nullable: true
-                  example:
+                  example: 
                 shipping_address:
                   type: object
                   nullable: true
@@ -190,7 +190,7 @@ components:
                   billing_address:
                     type: object
                     nullable: true
-                    example:
+                    example: 
                   shipping_address:
                     type: object
                     nullable: true
@@ -210,6 +210,9 @@ components:
                       country:
                         code: AU
                         name: Australia
+                  balance:
+                    type: number
+                    format: double
                 required:
                 - id
                 - enterprise_id
@@ -307,6 +310,12 @@ paths:
         in: query
         schema:
           type: string
+      - name: extra_fields[customer]
+        in: query
+        example: balance
+        description: Add extra fields to each customer
+        schema:
+          type: string
       responses:
         '200':
           description: Customers list
@@ -366,7 +375,7 @@ paths:
                 billing_address:
                   type: object
                   nullable: true
-                  example:
+                  example: 
                 shipping_address:
                   type: object
                   nullable: true
@@ -406,7 +415,120 @@ paths:
           content:
             application/json:
               schema:
-                "$ref": "#/components/schemas/customer"
+                type: object
+                properties:
+                  data:
+                    type: object
+                    properties:
+                      id:
+                        type: string
+                        example: '1'
+                      type:
+                        type: string
+                        example: customer
+                      attributes:
+                        type: object
+                        properties:
+                          id:
+                            type: integer
+                            example: 1
+                          enterprise_id:
+                            type: integer
+                            example: 2
+                          first_name:
+                            type: string
+                            nullable: true
+                            example: Alice
+                          last_name:
+                            type: string
+                            nullable: true
+                            example: Springs
+                          code:
+                            type: string
+                            nullable: true
+                            example: BUYER1
+                          email:
+                            type: string
+                            example: alice@example.com
+                          allow_charges:
+                            type: boolean
+                            example: false
+                          tags:
+                            type: array
+                            items:
+                              type: string
+                            example:
+                            - staff
+                            - discount
+                          terms_and_conditions_accepted_at:
+                            type: string
+                            format: date-time
+                            nullable: true
+                            example: '2022-03-12T15:55:00.000+11:00'
+                          billing_address:
+                            type: object
+                            nullable: true
+                            example: 
+                          shipping_address:
+                            type: object
+                            nullable: true
+                            example:
+                              phone: 0404 333 222 111
+                              latitude: -37.8173751
+                              longitude: 144.964803195704
+                              first_name: Alice
+                              last_name: Springs
+                              street_address_1: 1 Flinders Street
+                              street_address_2: ''
+                              postal_code: '1234'
+                              locality: Melbourne
+                              region:
+                                code: Vic
+                                name: Victoria
+                              country:
+                                code: AU
+                                name: Australia
+                          balance:
+                            type: number
+                            format: double
+                        required:
+                        - id
+                        - enterprise_id
+                        - first_name
+                        - last_name
+                        - code
+                        - email
+                        - allow_charges
+                        - tags
+                        - terms_and_conditions_accepted_at
+                        - billing_address
+                        - shipping_address
+                        - balance
+                      relationships:
+                        type: object
+                        properties:
+                          enterprise:
+                            type: object
+                            properties:
+                              data:
+                                type: object
+                                properties:
+                                  id:
+                                    type: string
+                                  type:
+                                    type: string
+                                    example: enterprise
+                              links:
+                                type: object
+                                properties:
+                                  related:
+                                    type: string
+                  meta:
+                    type: object
+                  links:
+                    type: object
+                required:
+                - data
         '404':
           description: Not found
           content:
@@ -476,7 +598,7 @@ paths:
                 billing_address:
                   type: object
                   nullable: true
-                  example:
+                  example: 
                 shipping_address:
                   type: object
                   nullable: true