Where to start debugging this problem

I have an EC2 instance that has a public IP address and I have ssh’ed into it, installed the httpd server and the gitlab runner. I have registered the runner and when I use the
# sudo gitlab-runner verify
Running in system-mode.
Verifying runner… is alive runner=196c1343
On my gitlab server I see:
image

But when I push a commit to the server, all I get is an email saying:
Your pipeline has failed.

A job entry never appears on the Jobs page.
How do I start to debug this?

Thanks

Turns out the .gitlab-ci.yml file was locked.