Visited McDonald’s tonight and when I tried to pay using my monzo card via the contactless terminal I received an “authorisation failed” message. Tried several more times and got the same message. So I used it with chip and pin and it worked fine. I have used it once before via contactless in the same restaurant without issues. For what it’s worth the non-monzo friends I was with had no issues using their contactless cards at the same time.
Best bet is to contact the in app support team and have them look into the transaction. That way they can find out what caused it and hopefully prevent it
We have lots of users who spend at McDonalds & I’ve used the card for contactless payments myself without any problems. So as Josh suggested, it’s worth asking support to look into this because if there was a general issue with contactless payments at McDonalds, it would have been discovered by now.