If a guest receives an email that says their reward will expire in 0 days, then a change will either need to be made to the Notification Template or the Redeemable.
If the Redeemable is set to 1 in the 'Remind before' field and your Notification Template uses the tag {{{remaining_days}}}, guests will receive an email that says their reward will expire in 0 days. The Redeemable will either need to be set to 2 (see When will Redeemable Expiry Notifications be sent out?) or the {{{remaining_days}}} will need to be updated to {{{reward_end_date}}}.
If further assistance is required, submit a ticket to Punchh Support. (For help submitting a ticket, click here)