The error " No Git consumers using SCM API plugin for: <Project URL>" occurs when you push changes to the GitLab repository and the webhook don't start the needed Jenkins job.
why it happened:
Jenkins don't find the project to build since the SSH URL is case sensitive and GitLab provide the URL in lowercase only.
How to solve:
Copy the Project name from GitLab and replace it at the SSH URL at the needed Jenkins job (Git section)