Can not add user via Release channel

We are UbiSim, a vendor on Applab, and that we have a client that we're trying to send release channel email invites to via the Meta developer page, but we are receiving an error that reads, 'We couldn't find anyone with the Oculus emails... etc." We have verified with the client that they have setup the emails on the headsets but yet we are still unable to send the invites out. We haven't had any other issues with other clients.