TestFlight is an app provided by Apple to allow users to test apps before making them publicly available in the App Store.
In order to be able to invite users as testers to TestFlight you first need to make sure the user is added to your App Store Connect account. Below you can find more details on how to invite a user to your App Store Connect account:
1 – After logging-in to your Apple Developer Account, access the “Users and Access” area: https://appstoreconnect.apple.com/access/users
2 – Click the “+” icon:
3 – Provide the user details in the modal window, select a role for the user and click “Invite” to invite the user to your account:
4 – The user will need to access his email and accept the invitation that was sent. Only once the invitation has been accepted you will be able to proceed with the next steps.
5 – Go to the “Apps” area (https://appstoreconnect.apple.com/apps) and select the app to which you would like to add the user as a tester:
6 – Click on “TestFlight”:
7 – Under “Internal Testing” click on the “App Store Connect Users” link:
8 – Under “Testers” click the “+” icon:
9 – On the modal window that appears, select the user that you would like to add as a tester to the app and click “add”
10 – The user will now receive an email from Apple with more details on how to proceed with installing “TestFlight” and adding the app to it for testing