Return epp error 2306 is tech are admin contacts are duplicated

app/models/epp/domain.rb

@@ -162,6 +162,9 @@ class Epp::Domain < Domain
     at[:admin_domain_contacts_attributes] = admin_domain_contacts_attrs(frame, action)
     at[:tech_domain_contacts_attributes] = tech_domain_contacts_attrs(frame, action)
 
+    check_for_same_contacts(at[:admin_domain_contacts_attributes], 'admin')
+    check_for_same_contacts(at[:tech_domain_contacts_attributes], 'tech')
+
     pw = frame.css('authInfo > pw').text
     at[:transfer_code] = pw if pw.present?
 
@@ -176,6 +179,11 @@ class Epp::Domain < Domain
     at
   end
 
+  def check_for_same_contacts(contacts, contact_type)
+    return unless contacts.uniq.count != contacts.count
+
+    add_epp_error('2306', contact_type, nil, %i[domain_contacts invalid])
+  end
 
   # Adding legal doc to domain and
   # if something goes wrong - raise Rollback error

test/integration/epp/domain/create/base_test.rb

@@ -142,12 +142,11 @@ class EppDomainCreateBaseTest < EppTestCase
       </epp>
     XML
 
-  
-
     assert_no_difference 'Domain.count' do
       post epp_create_path, params: { frame: request_xml },
            headers: { 'HTTP_COOKIE' => 'session=api_bestnames' }
     end
+
     assert_epp_response :parameter_value_policy_error
   end