Jenkins: No Git consumers using SCM API plugin for

The "No Git consumers using SCM API plugin for" messages is very confusing. It is spit out when post-commit triggers a build by http://localhost:8080/git/notifyCommit

If the errors are like:

No git jobs using repository: ...
No Git consumers using SCM API plugin for: ...

it does mean that the repository is not configured correctly for the project.

But if the messages are like:

Scheduled polling of ...
No Git consumers using SCM API plugin for: ...

you build may have actually been triggered.

Another confusing message is Authentication Failure. If you use a wrong URL for the post-commit, e.g. http://localhost:8080/jenkins/git/notifyCommit (with an extra "jenkins" inside), Jenkins won't tell you that notifyCommit is not found. Instead, it will say that you have an authentication failure.