Collabora Online Docker - Connection timed out

Hey Forum,

I have separated installations of nextcloud and collabora.
Now I tried to connect my nextcloud with the collabora instance but it fails with error:

GuzzleHttp\Exception\ConnectException: cURL error 7: Failed to connect to port 443: Connection timed out

When I try to access everything seems to be ok.

Maybe you have got an idea what I can try next?