Hey @kikorp78, welcome to the Glitch Forums!
I see that kikorp.ga is current associated with another project, which is why you can’t reuse it on a new project. that project hasn’t been deleted or removed, and removing it from the project has to be done from our end of things. We’ll need to know that project name and have some verification that you’re authorized to request its removal before processing that request (you might email email@example.com from an email associated with the domain or have an admin from that project do the same, for example).
As far as your login problems are concerned, that’s not related to the custom domain issue, which always has to be managed on our end of things. Do you see any errors when you try to log in? When is the last time you tried? We had a short-lived problem with Facebook logins last week that’s since been resolved, so if it’s been a few days you might just try again. Aside from that if you can provide your Glitch username I can see if there’s anything anything in our logs.