Mirror gitlab repo: access error

I have two gitlab accounts: my own (hollysully) and the one I have set up for my lab (CADEPP). My plan is to develop tasks on my personal account and push them to the lab account (which other people will eventually have access to).

CADEPP has forked & cloned repo ‘IGT’ from hollysully some days ago, but now I need to push the updated repo from hollysully to the forked CADEPP repo. I have added hollysully as a maintainer on the CADEPP IGT repo, and have tried setting up mirroring to push from the hollysully repo to the CADEPP repo, but I get this error:

image

Any advice appreciated!