Hi team
We have an issue when adding a guest to an activity.
If we enter a basic email address (such as user@domain.com) there is no issue:

However if the user has a subdomain (or two level top domain such as user@domain.co.nz or user@dept.domain.com) the option to select the guest disappears:

We have only come across this issue in iOS apps (iPhone and iPad) - web interface functions correctly.
Has anybody encountered this, or know of a workaround?
Thanks in advance,
Lance