I can’t add my custom domain due to this error:
The domain name is already added to a hosting account on our platform. Please remove your domain name from other free hosting providers and try again.
If you have two or three domain hosting account, then check if the cre8ivhouse.com.mk domain (the addon domain) is already in use with your other Infinityfree account.
Aside from Hetzner? What web hosting provider did you use before Hetzner? Did you use any other free web hosting provider by any chance? If so then can you tell us their brand name?
Nope, there was no other hosting than that. But maybe one year ago I have tried to add this domain to Infinitynet but I have never used it and now it’s not part of any account.
Then it seems like your domain was registered to that account where you tried to add your domain.
You may want to recheck it if you are still able to access it.