Just in case anyone comes across this. I was having the same problem. Because I'm new to it, I thought that I had to create the repository in GitHub first, and then match that name in Xcode when it asked for a repository name. So I'd created a repository called "smallnumber" in GitHub and then went to Xcode and when it asked for a repository name i typed in "smallnumber" and got the unknown error. Turns out, this was happening because that name was already taken, because I'd already created it in GitHub. When I used an entirely new name in Xcode for a repository that didn't exist yet, Xcode created the repository in GitHub automatically and pushed the project out.