Salutations Long,
I will need to investigate this further to see what is happening. I need you to try a few things:
1) Re-Send the invitation.
2) If they never received the invitation check the spam folder.
3) Try sending to another email.
4) If they receive it but there are issues with the link have the person receiving the invitation action it in an incognito window.
If the above does not work please send me a private reply with the following information:
A) What were the results of the above tests:
1)
2)
3)
4)
B) App ID
C) Email of the account used to send the invites.
D) List of people invites were sent to.
E) HAR files for sending and trying to use the link.
Thanks!