Refused to accept a valid McDonald’s voucher

Just left, as an extremely disappointed customer from McDonald’s Rivonia Village (South Africa). I tried to use a voucher for a Jalapeño chicken small meal - only to be told that “no the app does not work at this McDonalds”. I explained that the app should work at all McDonald’s and that they cannot just not fulfill a voucher when it is perfectly valid. I asked if she could still give me the same meal at the voucher price and she very rudely rep**** “no”. There was no level of customer care or effort here and I will most get not certainly not be returning.