Rewards Card will not link to app

I have been using Checkers Sixty60 for years now because it really is a great service. I've never had a complaint with the service itself but recently I've been feeling like I am losing out on a lot of the deals because on the app I am not a rewards member despite trying several times to register my card on the app. I've even tried getting a new card to register on the app with no success. It is very disappointing because despite knowing that I will not get any of the deals on offer I have still used the service but in these trying times I have to think economically and so I've since made the decision to use PnP ASAP because on that app I get all the deals that are on offer there is no prejudice.