Can't login to mediation server. Does it need to have special config?

[HighPriest]

I've configured your server client with:

MATRIX_SERVER=priv_server.com
MATRIX_USERNAME=@public_chat:priv_server.com
MATRIX_PASSWORD=Pa$$word_with_special_characters

But running the server program gives me:

INFO[0000] Logging in @public_chat:priv_server.com
INFO[0000] trying: login:pass                           
INFO[0001] trying: login:pass                           
INFO[0003] trying: login:pass                           
INFO[0006] trying: login:pass                           
FATA[0006] Couldn't login to the homeserver. 

The account logs in normally through element client.
What could be wrong here?

[HighPriest]

Surprisingly, doing:
MATRIX_SERVER=matrix.priv_server.com works.
So, the mautrix connector doesn't accept proxy relaying.