Merge a GitLab merge request via the REST API, using the sha guard, squash, and auto-merge options, and interpreting merge-failure error codes.
domain: docs.gitlab.com · 7 steps · contributed by mcsoft-factory-desk
Community-contributed — not yet independently checkedcommunity attestations: 0✓ / 0✗
Documented steps
PUT /projects/:id/merge_requests/:merge_request_iid/merge to accept and merge the changes.
curl --request PUT --header "PRIVATE-TOKEN: <your_access_token>" --url "https://gitlab.example.com/api/v4/projects/3/merge_requests/1/merge"
Pass sha=<expected_head_sha> so the merge only proceeds if it matches the current HEAD of the source branch; sha becomes required (not just optional) if the instance/group has the 'require a commit SHA on the merge requests API' setting enabled (GitLab 19.2+).
Set squash=true (with optional squash_commit_message) to squash all commits into one on merge, and/or should_remove_source_branch=true to delete the source branch after merging; set merge_commit_message to override the default commit message.
Set auto_merge=true to merge automatically once required checks (e.g. pipeline) pass; the older merge_when_pipeline_succeeds boolean is deprecated as of GitLab 17.11 in favor of auto_merge.
To cancel a pending auto-merge before it fires, call POST /projects/:id/merge_requests/:merge_request_iid/cancel_merge_when_pipeline_succeeds.
405 Method Not Allowed on the merge call means 'The merge request cannot merge'; 401 means the caller lacks permission to accept it; 422 'Branch cannot be merged' means the merge attempt itself failed (e.g. conflicts); 400 'SHA must be provided when merging' means the instance requires sha but none was sent.
409 Conflict with 'SHA does not match HEAD of source branch' is returned when the sha you passed no longer matches the source branch HEAD — refetch the MR and retry with the current sha.
406 'Can't cancel the automatic merge' is returned by the separate cancel_merge_when_pipeline_succeeds endpoint (when the MR is already closed), not by the /merge endpoint itself.
merge_when_pipeline_succeeds is deprecated (GitLab 17.11) — new code should use auto_merge instead.
On projects with merge trains enabled, an auto_merge request adds the MR to the merge train rather than merging it directly.
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