Hi AndroidFolk,
If you don't want to use email Id, you can use username and append it in any junk email domain to make email Id from it.
For example, if username is AndroidFolk, and your app name is MyApp, you can use email as AndroidFolk@MyApp.com and pass it to App42 User Service. You can use any other test/junk domain of your choice to make it work.
Let me know if it makes sense.