Server Setup but client gets unknown error 400 sync

I'm using this repo to build my server using the latest.

When I try to sync I get Unknown Error 400 when I click the "Check Synchronization Config"

Anyone had ideas?

I'm just another user but may I suggest that, if you want a bit of help from Joplin, you use the official Joplin server Docker image?

Edit:

Apologies, just noticed that this has already been mentioned when you raised the problem in another thread.