Invitation Email Not Received or Unusable
First ask support team, "Has the invitation been sent through Apple?" Do not mistake a business confirmation message for a TestFlight invitation.
Confirm Whether It Was Actually Sent
Ask support team to verify the registered email address, testable Build, external-testing eligibility, and invitation status. If the invitation has not been sent or the version is not yet available for testing, wait for support team to notify you. There is no need to reset the iPad.
Sent: Check the Email Address and Mail Categories
Search for TestFlight in the registered email account and check the spam and promotions folders. Verify the email address character by character with support team. If there is a typo, ask support team to correct it and resend the invitation. Do not forward the email directly to someone else for installation.
The Invitation Has Expired, Was Redeemed, or the Test Ended
Take a screenshot that records the exact message and time, then send it to support team so they can check the invitation and Build status. Ask support team to send a new invitation once the build is eligible for external testing. Do not guess codes, switch to an unfamiliar account, or ask to be added as a development team member to bypass external testing.
Hi Cheese Photo is not in TestFlight
First confirm that you have received a valid invitation from the company. If opening the email shows a redemption code, open TestFlight on the iPad, then open the sidebar, the account avatar at bottom-left, and "Redeem Invitation" in sequence, and enter the complete code. If it opens Hi Cheese Photo directly, accept and install it as prompted.
View the Complete Redemption Steps on iPad