Update and some clues.
In the last few days BOTH Panda and Grab are refusing my Bangkok Bank debit card which works elsewhere for scan payments, transfers on Lazada, etc.
Grab is saying contact the bank which I haven't bothered with as yet.
I tried entering the card again on Panda and with the second set of four digits got a problem with my card message so no point in proceeding.
Quite weird.
Surely this must be a widespread thing by now.
I'll eventually call them, paying cash for now, maybe I'll try another card, but if you have called Bangkok Bank on this issue, what's up?