Grab in Malaysia have stopped accepting Visa for Grab top up and I believe Grab Wallet. You can still use the Grab app and elect to pay cash at the time of booking. I have yet to determine whether Visa can be used for individual fares on a ride by ride basis, but if flying there, best to have some local cash to hand.

Edit to clarify a poorly articulated subject line by me - Mastercard and Amex are STILL accepted for top up.