User Profile

We have recently rolled out a one-time-password only log in system for our app. Access to our app is by invite only and users are required to register outside of the app to set up their account (it is an app for events & conferences). The majority of users have requested this login system as it is more secure and easier than a traditional password. I submitted the app for review, but it was rejected as the Apple tester required the email access code that was sent when they entered the tester email address we have in the app description. Does anyone have any advice on how we can remedy this so that our app does not keep getting rejected for this reason? Thanks