The heartbeat message just means that it can talk to the master server. It probably is your firewall that is blocking incoming traffic from the clients now.
I'm actually glad there's a Proton Drive link for this mod.
More modders should use Proton Drive instead of Google, but I think it's my FOSS brain being... well, my FOSS brain.
@Marto-GOD create your own topic, this is a 2 years old topic.
On your topic explain the issue properly. Also this error and how to not get it is documented, just read the install doc
