Cannot configure Gitea server

[holgerflick]

I have set up my Gitea instance at https://git.flixments.com . It works perfectly. I created a token but if I test connecting from Gitea Mirror, the software tells me it fails. A more detailed error message I get if I actually try to mirror a repository:

Repository x failed to mirror. Error: Network error: unable to verify the first certificate

I created Gitea and Gitea Mirror using Dokploy inside of a project. Gitea Mirror is hosted on mirror.flixments.com.

I found the certs/README.md but that does not help me at all as all certificates are handled by Dokploy and I usually cannot access them. As there is a Dokploy template I am pretty sure somebody was able to get this to work.

The certificate is downloaded from Ionos.com. I think they use Let's Encrypt to provide certificates. I think this should work out of the box tbh.

Any hints?