Can't config Google account without Gmail/Email

Hello, I am trying to set up my iPhone 6S.

But it looks as if it is not possible to use a Google account that doesn't use a Gmail adress? I am using a Google account with an GMX adress, for calender purposes (originally, this was a Youtube account that has been upgraded to a Google account).

One year ago, I set up an iPhone 6 and iPad Air 2, both released with iOS 8.0. It worked without any problems.

But there must have been changes (or a bug) between iOS 8.1 and 8.3, and still in iOS 9.

Other people seem to have that issue, too:

http://apple.stackexchange.com/questions/182142/adding-a-google-account-for-cale ndar-purposes-on-ios-8-3

Entering the password - okay. So I am confident that I entered the correct password.

Then, the "accept" screen appears. Still, everything is okay.

After that, the "feature select" screen appears for a very short period. All switches are greyed off, and than I am thrown back to the "add account" screen.

There is no error message.

Is there a chance that Apple might fix this bug?