If you get the error message "The guest could not be reactivated", you'll want to check for an account with the email address minus the deactivated portion as there cannot be multiple guest accounts with the same email.
For example, I have an account with a test email. When I deactivate this account, the email will now read deactivated-[email]. This will allow the email to be reused to create an account. However, if this happens and you then try to reactivate the deactivated guest, you will receive the error message.
If further assistance is required, submit a ticket to Punchh Support. (For help submitting a ticket, click here)