Highly Embarresed - Could not redeem voucher at Tyler's Umdloti

We received a Dineplan Voucher and after researching and booking via the Dineplan App at a Restaurant listed as a participating which was Tyler's Umdloti, We were extremely disappointed and embarrassed that when it came to paying the Bill, The Restaurant did not accept the Voucher, this after checking in with the Restaurant on 2 separate occasions as well as the Waitress prior to us ordering