Login problem (fqn/IP)?

HI,

I run nextcloud in a docker container. To get htps working I have apace on the host machine.

I am able to access the nextcloud site via IP address and fqn. So probably I configured some stuff correctly.
Login via IP address is working. I can create users and use the accounts.

Login via fqn is not possible. I am redirected to the login page. Some tries later login is slowed down.

Adding ‘overwritehostqq’ (with fqn) is not helping. The result is I am not able to login via IP or fqn.
Resetting the login is not helping, too.

So, any help is welcome.