Update delete contract to use same error messages

app/contracts/relations/delete_contract.rb

@@ -30,14 +30,14 @@
 
 module Relations
   class DeleteContract < ::DeleteContract
-    delete_permission -> { user.allowed_in_work_package?(:manage_work_package_relations, model.from) }
+    delete_permission -> {
+      user.allowed_in_work_package?(:manage_work_package_relations, model.from) &&
+        user.allowed_in_work_package?(:manage_work_package_relations, model.to)
+    }
 
-    validate :validate_to_deletable
-
-    def validate_to_deletable
-      return unless user.allowed_in_work_package?(:manage_work_package_relations, model.from)
-
-      unless user.allowed_in_work_package?(:manage_work_package_relations, model.to)
+    # Override method to add more specific error
+    def user_allowed
+      unless authorized?
         errors.add :base, :error_not_deletable
       end
     end

spec/contracts/relations/delete_contract_spec.rb

@@ -73,13 +73,13 @@ RSpec.describe Relations::DeleteContract do
              })
     end
 
-    it_behaves_like "contract is invalid", base: :error_unauthorized
+    it_behaves_like "contract is invalid", base: :error_not_deletable
   end
 
   context "when user has no permissions for either work package" do
     let(:current_user) { create(:user) }
 
-    it_behaves_like "contract is invalid", base: :error_unauthorized
+    it_behaves_like "contract is invalid", base: :error_not_deletable
   end
 
   context "when user is an admin" do

spec/requests/api/v3/relations/relations_api_spec.rb

@@ -401,8 +401,8 @@ RSpec.describe "API v3 Relation resource", content_type: :json do
     context "lacking the permission" do
       let(:permissions) { %i[view_work_packages] }
 
-      it "returns 403" do
-        expect(last_response).to have_http_status :forbidden
+      it "returns 422" do
+        expect(last_response).to have_http_status :unprocessable_entity
       end
 
       it "leaves the relation" do