Display no shipping method selected error

app/assets/stylesheets/darkswarm/split-checkout.scss

@@ -103,6 +103,10 @@
       padding-right: 5px;
       padding-top: 2px;
       padding-bottom: 2px;
+
+      &.standalone {
+        padding: 10px;
+      }
     }
 
     #distributor_address.panel {

app/controllers/split_checkout_controller.rb

@@ -39,6 +39,9 @@ class SplitCheckoutController < ::BaseController
       advance_order_state
       redirect_to_step
     else
+      if params[:shipping_method_id].blank?
+        @order.errors.add(:base, "no_shipping_method_selected")
+      end
       flash.now[:error] = "Saving failed, please update the highlighted fields"
       render :edit
     end

app/views/split_checkout/_details.html.haml

@@ -68,6 +68,10 @@
     = t("split_checkout.step1.delivery_address.title")
 
   - selected_shipping_method = @order.shipping_method&.id
+  - if selected_shipping_method == nil && @order.errors.messages_for(:base).include?("no_shipping_method_selected")
+    %div.checkout-input
+      %span.formError.standalone
+        = t("split_checkout.step1.delivery_address.errors.no_shipping_method_selected")
   - @shipping_methods.each do |shipping_method|
     %div.checkout-input
       = fields_for shipping_method do |shipping_method_form|

config/locales/en.yml

@@ -1660,6 +1660,8 @@ en:
           label: Country
       delivery_address:
           title: Delivery address
+          errors:
+            no_shipping_method_selected: No shipping method selected
       submit: Next - Payment method
       cancel: Back to Edit basket
     step2: