diff --git a/lib/api/commits.rb b/lib/api/commits.rb
index 8e528e266bf3fe92d4fadbeaafb1b4d39e848d56..0de4e720ffe00ca8c8af9b0746e234b7d0ac3902 100644
--- a/lib/api/commits.rb
+++ b/lib/api/commits.rb
@@ -108,7 +108,7 @@ module API
         if note.save
           present note, with: Entities::CommitNote
         else
-          render_api_error!("Failed to save note #{note.errors.messages}", 422)
+          render_api_error!("Failed to save note #{note.errors.messages}", 400)
         end
       end
     end
diff --git a/lib/api/deploy_keys.rb b/lib/api/deploy_keys.rb
index 06eb7756841fe4ef5540bfef81480cb6fd2ddda5..dd4b761feb2629fa9638553377c16e03e6f9b0dd 100644
--- a/lib/api/deploy_keys.rb
+++ b/lib/api/deploy_keys.rb
@@ -58,7 +58,7 @@ module API
         if key.valid? && user_project.deploy_keys << key
           present key, with: Entities::SSHKey
         else
-          render_validation_error!(key)
+          render_api_error!("Failed to add key #{key.errors.messages}", 400)
         end
       end
 
diff --git a/lib/api/groups.rb b/lib/api/groups.rb
index cee51c82ad5914095f0cd1afe99702944d29f82f..bda60b3b7d53aa3e49841e4ae4d297800da8d6ad 100644
--- a/lib/api/groups.rb
+++ b/lib/api/groups.rb
@@ -54,7 +54,7 @@ module API
         if @group.save
           present @group, with: Entities::Group
         else
-          render_api_error!("Failed to save group #{@group.errors.messages}", 422)
+          render_api_error!("Failed to save group #{@group.errors.messages}", 400)
         end
       end
 
@@ -97,7 +97,7 @@ module API
         if result
           present group
         else
-          render_api_error!("Failed to transfer project #{project.errors.messages}", 422)
+          render_api_error!("Failed to transfer project #{project.errors.messages}", 400)
         end
       end
     end
diff --git a/lib/api/issues.rb b/lib/api/issues.rb
index d2828b24c369c63bc0eff1b8f130dca03d439f24..01496c399557ae8092502700d549dcaf26996adc 100644
--- a/lib/api/issues.rb
+++ b/lib/api/issues.rb
@@ -104,7 +104,7 @@ module API
 
         # Validate label names in advance
         if (errors = validate_label_params(params)).any?
-          render_api_error!({ labels: errors }, 400)
+          render_api_error!("Unable to validate label: #{errors}"}, 400)
         end
 
         issue = ::Issues::CreateService.new(user_project, current_user, attrs).execute
@@ -118,7 +118,7 @@ module API
 
           present issue, with: Entities::Issue
         else
-          render_validation_error!(issue)
+          render_api_error!("Unable to create issue #{issue.errors.messages}", 400)
         end
       end
 
@@ -142,7 +142,7 @@ module API
 
         # Validate label names in advance
         if (errors = validate_label_params(params)).any?
-          render_api_error!({ labels: errors }, 400)
+          render_api_error!("Unable to validate label: #{errors}"}, 400)
         end
 
         issue = ::Issues::UpdateService.new(user_project, current_user, attrs).execute(issue)
@@ -158,7 +158,7 @@ module API
 
           present issue, with: Entities::Issue
         else
-          render_validation_error!(issue)
+          render_api_error!("Unable to update issue #{issue.errors.messages}", 400)
         end
       end
 
diff --git a/lib/api/labels.rb b/lib/api/labels.rb
index 78ca58ad0d13462b83473724cdb169eef4673e09..e8ded66225341bbdc10e943196413093bc8c5e06 100644
--- a/lib/api/labels.rb
+++ b/lib/api/labels.rb
@@ -37,7 +37,7 @@ module API
         if label.valid?
           present label, with: Entities::Label
         else
-          render_validation_error!(label)
+          render_api_error!("Unable to create label #{label.errors.messages}", 400)
         end
       end
 
@@ -90,7 +90,7 @@ module API
         if label.update(attrs)
           present label, with: Entities::Label
         else
-          render_validation_error!(label)
+          render_api_error!("Unable to create label #{label.errors.messages}", 400)
         end
       end
     end
diff --git a/lib/api/merge_requests.rb b/lib/api/merge_requests.rb
index a365f1db00f6f07ad4c6fba2fd75a8725e89a3db..1a73c4943b8f73906188ff35890b6ae84cffccea 100644
--- a/lib/api/merge_requests.rb
+++ b/lib/api/merge_requests.rb
@@ -137,7 +137,7 @@ module API
 
         # Validate label names in advance
         if (errors = validate_label_params(params)).any?
-          render_api_error!({ labels: errors }, 400)
+          render_api_error!("Unable to validate label: #{errors}"}, 400)
         end
 
         merge_request = ::MergeRequests::UpdateService.new(user_project, current_user, attrs).execute(merge_request)
@@ -233,7 +233,7 @@ module API
         if note.save
           present note, with: Entities::MRNote
         else
-          render_validation_error!(note)
+          render_api_error!("Failed to save note #{note.errors.messages}", 400)
         end
       end
     end
diff --git a/lib/api/milestones.rb b/lib/api/milestones.rb
index 4d79f5a69ae40194b84d1b6e2ccb11b1db14ab41..2ea49359df00edd128d64ad59fe4d15c136f35d2 100644
--- a/lib/api/milestones.rb
+++ b/lib/api/milestones.rb
@@ -48,7 +48,7 @@ module API
         if milestone.valid?
           present milestone, with: Entities::Milestone
         else
-          not_found!("Milestone #{milestone.errors.messages}")
+          render_api_error!("Failed to create milestone #{milestone.errors.messages}", 400)
         end
       end
 
@@ -72,7 +72,7 @@ module API
         if milestone.valid?
           present milestone, with: Entities::Milestone
         else
-          not_found!("Milestone #{milestone.errors.messages}")
+          render_api_error!("Failed to update milestone #{milestone.errors.messages}", 400)
         end
       end
     end
diff --git a/lib/api/notes.rb b/lib/api/notes.rb
index b04d623c695493dc5b6343d48e7601a33e6934b0..3726be7c5374c151be3e9db957a4be886b3d3537 100644
--- a/lib/api/notes.rb
+++ b/lib/api/notes.rb
@@ -93,7 +93,7 @@ module API
           if @note.valid?
             present @note, with: Entities::Note
           else
-            bad_request!('Invalid note')
+            render_api_error!("Failed to save note #{note.errors.messages}", 400)
           end
         end