So far I saw YouTrip is specifically excluded from Citibank and UOB card. But it worked for Standard Chartered Unlimited Cashback. I've tried and gotten 1.5% cashback on all my YouTrip top-ups with that card, at least at the of time of this post. Hope it helps!
Think they found out about it and have since excluded it from the cashback calculations.
Went to research on the MCC and found out that it is 6540 (Non-Financial Institutions – Stored Value Card Purchase/Load)
I'm not sure which credit card or bank that has rewards for topping up Youtrip (if that is what you meant) but I would love to know!