Any of the above solutions worked for me. Instead of using the “Share” button which provides you with an URL of this kind: https://glitch.com/~solid-stop (solid-stop is the name of my project) I’d rather suggest to use the following.
This issue is still ongoing. I tried everything above and nothing worked. The issue is Glitch is not importing the files from Git, whether you use the link or if you go to git and copy the .git link.
The only thing that worked for me was to manually copy and paste all the files over from git to glitch.
I had the same problem. First I was getting the “JSON” error cause I was copying the wrong URL. Then I started getting the “Timeout” error. As @dkimble said above, the only thing that worked was manually copy and paste everything from git to the glitch project.