I am pretty certain that this issue is not GeneratePress related, but because your support absolutely rocks I try anyway.
I installed the plugin schema ninja which has a free version and a pro one. To use the free one I had to visit their homepage to get a key for the free version. When I try to authorize it, I don’t get an error message or anything else, the page partially reloads and that’s it. Can this be caused by generatepress or wordpress multisite?