I had problems when adding users simple because i was copying emails with a space at the end...your app does not allow it.
I found the issue after logging in and after creating some projects. I was trying to add some users to the projects (via the rightmost "plus" menu). It took me a while to figure this out because from gmail's search bar, not the browser's, if you type a partial email and have google fill the rest AND COPY IT, it will come with a space at the end.