Trigger pipeline via API returns 404

Summary

Triggering a pipeline through the API with a PAT with all scopes returns a 404 error.

Steps to reproduce

1. Create a project on GitLab.com.
2. Add a .gitlab-ci.yml file.
3. Generate a PAT with at least api + write_repository scopes or check all of them for good measure.
4. Run a cURL request to trigger a pipeline.
5. Observe 404 error.

Example Project

• gitlab-gold/trigger-pipeline-api

What is the current bug behavior?

A 404 error is returned.

What is the expected correct behavior?

A pipeline in the specified project should be triggered.

Relevant logs and/or screenshots

API call being used:

curl --request POST \
     --form token=<token-removed> \
     --form ref=master \
     https://gitlab.com/api/v4/projects/15174910/trigger/pipeline

Output:

{"message":"404 Not Found"}

Output of checks

This bug happens on GitLab.com: 12.5.0-pre 4760421fb44

ZD: https://gitlab.zendesk.com/agent/tickets/137559 (GitLab Internal)