Not a happy customer

Me and my colleague went to the Mcdonalds in Stoneridge to buy food today, we had the food on the app for discount and when we got there we were told that they can't redeem the voucher because the system had a problem and it's a global issue and it has been going on for a week. If it's a global issue couldn't your Head Office create a manual way of redeeming or rather remove all the specials from the app? It was our lunch time and we pressed on time so to come across this and they say there's no way they can assist us unless we buy on a full price.. What's the use of having the app then? But yet when they ask us to rate the store it becomes easy... It always happens that l in most cases am not happy with the McDonald service or something doesn't go right and it doesn't look like the Head Office cares or even take care of their customers. I am not happy at all. Please inform me about what will be done about this issue on *** or ***