Now that after latest update from Apple for iTunes, Apps option is removed from Library in iTunes.
See Article Here: https://support.apple.com/en-us/HT208075
How should my client, now get the ad hoc IPA, installed to his iPhone. Do the developers now need to deliver through TestFlight beta testing only?
You can still install ad-hoc apps using iTunes by following the steps under Manually add items from your computer in this tech note
The steps are: