That project is already taken, which is why it’s not letting you register it. I’ll raise a bug for the UI not showing that for some reason in this case. Sorry about that.
Hello, I have a similar, maybe related problem. I have renamed a project, then after some time deleted it. Now I created the project again, tried to assign the name I had assigned it before, and it keeps on saying that the name is taken. Of course if I visit the page https://>name<.glitch.me, it says that the project does not exist, but I still cannot assign it the name I want.
Since the name it is not actually taken, I thing this is a bug. The name should be freed immediately after a project is renamed OR deleted. Or at least this is what I would expect.
Please let me know if there is a way to get my name back, or if it is doomed to stay in the “already-taken-but-not-really” limbo forever.