Tap to Pay was giving up after 3 seconds while it was still getting the reader ready. Getting ready needs the internet, so out on a job it often ran out of time and the tap did nothing, even though the phone and the card were both fine. It now waits up to 25 seconds.
Tap to Pay now tells you why a card did not work: not enough funds, wrong PIN, card expired, card locked after too many PIN tries, or card over its limit. Before, every one of these read as the same "could not take this payment".