Become a beta tester for farmOS Field Kit on iOS (et al)

Hi, i cannot Login to my farmos server with field kit. I always get
“Unable to reach the server. Please check that you have the correct URL and that your device has a network connection. Status: Request failed with status code 403”
I’m pretty sure that URL, user and password are correct as I’m using a password manager.
Trying Android or Webapp of Field Kit lead to same results.
I’m using version 0.4.9
I’m running farmos in a docker and use traefik as a reverse proxy.
My URL is like farmos.mydomain.de if that’s relevant.
Can someone help me find out what’s the issue?