Allow for creating a voucher with either flat or percentage rate

In the scenario when you get an error when trying to create a
percentage voucher, on the subsequent try we would be dealing with
a "percentage rate voucher". The code now handle any type of voucher

app/controllers/admin/vouchers_controller.rb

@@ -9,9 +9,13 @@ module Admin
     end
 
     def create
+      # In the scenario where you get an error when trying to create a percentage voucher, we'll
+      # now have percentage rate voucher instanciated. Hence why we check for both params type
+      voucher_type = params.dig(:vouchers_flat_rate, :voucher_type) ||
+                     params[:vouchers_percentage_rate][:voucher_type]
+
       # The use of "safe_constantize" here will trigger a Brakeman error, it can safely be ignored
       # as it's a false positive : https://github.com/openfoodfoundation/openfoodnetwork/pull/10821
-      voucher_type = params[:vouchers_flat_rate][:voucher_type]
       if Voucher::TYPES.include?(voucher_type)
         @voucher = voucher_type.safe_constantize.create(
           permitted_resource_params.merge(enterprise: @enterprise)
@@ -44,7 +48,11 @@ module Admin
     end
 
     def permitted_resource_params
-      params.require(:vouchers_flat_rate).permit(:code, :amount)
+      if params[:vouchers_flat_rate].present?
+        return params.require(:vouchers_flat_rate).permit(:code, :amount)
+      end
+
+      params.require(:vouchers_percentage_rate).permit(:code, :amount)
     end
   end
 end

spec/requests/admin/vouchers_controller_spec.rb

@@ -50,6 +50,15 @@ describe Admin::VouchersController, type: :request do
     end
 
     context "with a percentage rate voucher" do
+      let(:params) do
+        {
+          vouchers_percentage_rate: {
+            code: code,
+            amount: amount,
+            voucher_type: type
+          }
+        }
+      end
       let(:type) { "Vouchers::PercentageRate" }
 
       it "creates a new voucher" do