Marking a MR for Merge-When-Pipeline-Succeeds fails directly after creating the MR

Everyone can contribute. Help move this issue forward while earning points, leveling up and collecting rewards.

• Close this issue

Summary

Trying to "merge when pipeline succeeds" via the API, immediately after opening a MR, fails with "405 Method not allowed".

Steps to reproduce

1. POST /projects/:id/merge_requests
2. Use the resulting MR iid to run PUT /projects/:id/merge_requests/:iid/merge with merge_when_pipeline_succeeds=true

Example Project

We're using CML to automatically create merge requests with new data that is pulled in daily (example). We'd like to automatically mark them as "merge when pipeline succeeds", and I opened a PR to CML that adds this behaviour: https://github.com/iterative/cml/pull/903

What is the current bug behavior?

It responds 405 Method Not allowed

What is the expected correct behavior?

It responds 200 OK

Relevant logs and/or screenshots

Output of checks

Results of GitLab environment info

this bug happens on gitlab.com

Possible fixes

on my end, I can fix it by adding a 20secs timeout between the two API calls. this makes me think there's some race condition with a background worker on Gitlab's side that hasn't yet executed.