I am a member of my company\'s development team, with the role of Admin. I can access the Member Center of the team at https://developer.apple.com/
However, when I I
I had similar issues and I got quite a few random answers from iTunesConnect support until I managed to get an iTunes Connect supervisor.
Here is what is happening:
This 'initialise' is key:
Apple DOES NOT know the user but they have enough details to set a skeleton account allowing the user to login.
To turn this into a real/complete account, the user has to log in to appleid.apple.com, add birth date AND answer/set the security questions.
Once that is done, the account will become a fully fledged account.
Then, if you send an invite (and if they user did not give up and switched to Android), when he/she accepts/clicks on the invitation, they will be set up as expected.
Good luck!
p.s. I'm the iTunesConnect guy in my company...