diff --git a/app/controllers/repp/v1/base_controller.rb b/app/controllers/repp/v1/base_controller.rb
index f8a465e77..b3aa786d1 100644
--- a/app/controllers/repp/v1/base_controller.rb
+++ b/app/controllers/repp/v1/base_controller.rb
@@ -59,9 +59,12 @@ module Repp
         end
       end
 
-      def render_epp_error(status = :bad_request)
+      def render_epp_error(status = :bad_request, data = {})
+        @epp_errors ||= []
+        @epp_errors << { code: 2304, msg: 'Command failed' } if data != {}
+
         render(
-          json: { code: @epp_errors[0][:code], message: @epp_errors[0][:msg] },
+          json: { code: @epp_errors[0][:code], message: @epp_errors[0][:msg], data: data },
           status: status
         )
       end
diff --git a/app/controllers/repp/v1/domains/contacts_controller.rb b/app/controllers/repp/v1/domains/contacts_controller.rb
index 226981b60..70f64ed28 100644
--- a/app/controllers/repp/v1/domains/contacts_controller.rb
+++ b/app/controllers/repp/v1/domains/contacts_controller.rb
@@ -16,12 +16,15 @@ module Repp
         end
 
         def update
-          @epp_errors << { code: '2304', msg: 'New contact must be valid' } if @new_contact.invalid?
+          @epp_errors ||= []
+          @epp_errors << { code: 2304, msg: 'New contact must be valid' } if @new_contact.invalid?
 
           if @new_contact == @current_contact
-            @epp_errors << { code: '2304', msg: 'New contact must be different from current' }
+            @epp_errors << { code: 2304, msg: 'New contact must be different from current' }
           end
 
+          return handle_errors if @epp_errors.any?
+
           affected, skipped = TechDomainContact.replace(@current_contact, @new_contact)
           data = { affected_domains: affected, skipped_domains: skipped }
           render_success(data: data)
diff --git a/app/controllers/repp/v1/domains_controller.rb b/app/controllers/repp/v1/domains_controller.rb
index 237ed5fe4..163731c69 100644
--- a/app/controllers/repp/v1/domains_controller.rb
+++ b/app/controllers/repp/v1/domains_controller.rb
@@ -34,7 +34,7 @@ module Repp
         end
 
         if @errors.any?
-          render_success(data: { errors: @errors })
+          render_epp_error(:bad_request, @errors)
         else
           render_success(data: @successful)
         end
@@ -52,10 +52,11 @@ module Repp
         domain = Domain.find_by(name: domain_name)
         # rubocop:disable Style/AndOr
         add_error("#{domain_name} does not exist") and return unless domain
-        valid_transfer_code = domain.transfer_code.eql?(transfer_code)
-        add_error("#{domain_name} transfer code is wrong") and return unless valid_transfer_code
         # rubocop:enable Style/AndOr
-
+        unless domain.transfer_code.eql?(transfer_code)
+          add_error("#{domain_name} transfer code is wrong")
+          return
+        end
         domain
       end
 
diff --git a/app/controllers/repp/v1/registrar/nameservers_controller.rb b/app/controllers/repp/v1/registrar/nameservers_controller.rb
index 7e00cf2ac..1af85b760 100644
--- a/app/controllers/repp/v1/registrar/nameservers_controller.rb
+++ b/app/controllers/repp/v1/registrar/nameservers_controller.rb
@@ -22,7 +22,7 @@ module Repp
 
         def hostname_params
           params.require(:data).require(%i[type id])
-          params.require(:data).require(:attributes)
+          params.require(:data).require(:attributes).require([:hostname])
 
           params.permit(data: [:type, :id, attributes: [:hostname, ipv4: [], ipv6: []]])
         end
diff --git a/test/integration/api/domain_contacts_test.rb b/test/integration/api/domain_contacts_test.rb
index 5336cc10a..6704739d1 100644
--- a/test/integration/api/domain_contacts_test.rb
+++ b/test/integration/api/domain_contacts_test.rb
@@ -27,8 +27,8 @@ class APIDomainContactsTest < ApplicationIntegrationTest
           headers: { 'HTTP_AUTHORIZATION' => http_auth_key }
 
     assert_response :ok
-    assert_equal ({ affected_domains: %w[airport.test shop.test],
-                    skipped_domains: [] }),
+    assert_equal ({ code: 1000, message: 'Command completed successfully', data: { affected_domains: %w[airport.test shop.test],
+                    skipped_domains: [] }}),
                  JSON.parse(response.body, symbolize_names: true)
   end
 
@@ -42,7 +42,7 @@ class APIDomainContactsTest < ApplicationIntegrationTest
 
     assert_response :ok
     assert_equal %w[airport.test shop.test], JSON.parse(response.body,
-                                                        symbolize_names: true)[:skipped_domains]
+                                                        symbolize_names: true)[:data][:skipped_domains]
   end
 
   def test_keep_other_tech_contacts_intact
@@ -66,10 +66,8 @@ class APIDomainContactsTest < ApplicationIntegrationTest
                                                  new_contact_id: 'william-002' },
           headers: { 'HTTP_AUTHORIZATION' => http_auth_key }
 
-    assert_response :bad_request
-    assert_equal ({ error: { type: 'invalid_request_error',
-                             param: 'current_contact_id',
-                             message: 'No such contact: jack-001' } }),
+    assert_response :not_found
+    assert_equal ({ code: 2303, message: 'Object does not exist' }),
                  JSON.parse(response.body, symbolize_names: true)
   end
 
@@ -77,10 +75,8 @@ class APIDomainContactsTest < ApplicationIntegrationTest
     patch '/repp/v1/domains/contacts', params: { current_contact_id: 'non-existent',
                                                  new_contact_id: 'john-001' },
           headers: { 'HTTP_AUTHORIZATION' => http_auth_key }
-    assert_response :bad_request
-    assert_equal ({ error: { type: 'invalid_request_error',
-                             param: 'current_contact_id',
-                             message: 'No such contact: non-existent' } }),
+    assert_response :not_found
+    assert_equal ({ code: 2303, message: 'Object does not exist' }),
                  JSON.parse(response.body, symbolize_names: true)
   end
 
@@ -88,10 +84,8 @@ class APIDomainContactsTest < ApplicationIntegrationTest
     patch '/repp/v1/domains/contacts', params: { current_contact_id: 'william-001',
                                                  new_contact_id: 'non-existent' },
           headers: { 'HTTP_AUTHORIZATION' => http_auth_key }
-    assert_response :bad_request
-    assert_equal ({ error: { type: 'invalid_request_error',
-                             param: 'new_contact_id',
-                             message: 'No such contact: non-existent' } }),
+    assert_response :not_found
+    assert_equal ({code: 2303, message: 'Object does not exist'}),
                  JSON.parse(response.body, symbolize_names: true)
   end
 
@@ -100,9 +94,7 @@ class APIDomainContactsTest < ApplicationIntegrationTest
                                                  new_contact_id: 'invalid' },
           headers: { 'HTTP_AUTHORIZATION' => http_auth_key }
     assert_response :bad_request
-    assert_equal ({ error: { type: 'invalid_request_error',
-                             param: 'new_contact_id',
-                             message: 'New contact must be valid' } }),
+    assert_equal ({ code: 2304, message: 'New contact must be valid', data: {} }),
                  JSON.parse(response.body, symbolize_names: true)
   end
 
@@ -111,8 +103,7 @@ class APIDomainContactsTest < ApplicationIntegrationTest
                                                  new_contact_id: 'william-001' },
           headers: { 'HTTP_AUTHORIZATION' => http_auth_key }
     assert_response :bad_request
-    assert_equal ({ error: { type: 'invalid_request_error',
-                             message: 'New contact ID must be different from current contact ID' } }),
+    assert_equal ({ code: 2304, message: 'New contact must be different from current', data: {} }),
                  JSON.parse(response.body, symbolize_names: true)
   end
 
diff --git a/test/integration/api/domain_transfers_test.rb b/test/integration/api/domain_transfers_test.rb
index ce6235268..ecb69d262 100644
--- a/test/integration/api/domain_transfers_test.rb
+++ b/test/integration/api/domain_transfers_test.rb
@@ -90,7 +90,7 @@ class APIDomainTransfersTest < ApplicationIntegrationTest
          as: :json,
          headers: { 'HTTP_AUTHORIZATION' => http_auth_key }
     assert_response 400
-    assert_equal ({ errors: [{ title: 'non-existent.test does not exist' }] }),
+    assert_equal ({ code: 2304, message: 'Command failed', data: [{ title: 'non-existent.test does not exist' }] }),
                  JSON.parse(response.body, symbolize_names: true)
   end
 
@@ -102,7 +102,7 @@ class APIDomainTransfersTest < ApplicationIntegrationTest
          headers: { 'HTTP_AUTHORIZATION' => http_auth_key }
     assert_response 400
     refute_equal @new_registrar, @domain.registrar
-    assert_equal ({ errors: [{ title: 'shop.test transfer code is wrong' }] }),
+    assert_equal ({ code: 2304, message: 'Command failed', data: [{ title: 'shop.test transfer code is wrong' }] }),
                  JSON.parse(response.body, symbolize_names: true)
   end