As a consultant, I’ve had this situation come up many times, and it’s very frustrating because Apple doesn’t allow an Apple ID to belong to more than one iTunes Connect account.
The scenario is that you have a client or friend that you would like to be an internal tester in your organization’s iTunes Connect account, or, perhaps it’s the corollary situation in which you have a client who has their own iTunes Connect account and you need access to their account as a tester or admin or developer. I’ve had this situation come up both ways, and here is how I’ve dealt with it.
The main requirement is that your prospective tester has a Gmail account. I’m not sure if this trick works with other email systems but it definitely works with Gmail. So if they they do, then you should be good to go. These days most individuals and companies are using Gmail as their provider so I haven’t run into anyone that this didn’t work with yet.
On with the process!
In nutshell, to circumvent Apple’s crazy limitation, you can do the “+appname” trick on their Gmail email address. For example, if the person I want to add is “firstname.lastname@example.org”, and the name of the app I’m working on is “Awesome App” I would send him an invitation as “email@example.com”. Their Gmail-based mail system will let the email through just fine.
Then, they create a new, separate Apple ID with “firstname.lastname@example.org”, and iTunes doesn’t complain. iTunes Connect emails get sent to the right place because Gmail just treats them as the same account, and then your client (or you) can have multiple iTunes Connect accounts with what amounts to the same email address.
Then when they receive the follow-up notification to join TestFlight, it arrives at the right email address, and when they tap the button in the email it opens TestFlight on their device, they sign in with their normal Apple ID (even if it’s email@example.com), and then they’re in.
It feels a bit hackish, but it works!
I’m pretty sure I learned this technique from this blog post, which also has some other great suggestions for working with clients and getting their builds up to the App Store, which is a subject for another day…