Duplicating my own respond from another post: here was my solution:
Sorry if this has already been answered. I found my solution: say you’ve got a private group G with projects P1 and P2. P1 includes submodule …/P2.
Toy need to go into the P2 projects settings, under CI/CD settings (NOT PERMISSIONS ! Which is what threw me). Under the CICD settings, you go to something like “pipeline tokens” or something. I have no power now and 0.2 mbits/sec on my phone, so can’t easily check exactly.
But under P2->settings->CI/CD->pipeline token, add the group GitLab.COM/myname/G/P1. This gives the P1 pipeline access to clone the P2 project.
This must be a new feature