I can use the highest cashback credit card to topup grabpay credits.
eg. topup $2000 using HSBC CC and earned 2.5% = $50
I'm a Platinum member, $1 grabpay spent earned 10pts, $2000 earned 20,000 pts.
pts earned can be used to buy stuff or purchase $10 grabride vouchers for 3600 pts, 20,000 pts I can purchase $10 x5 vouchers + $5 x1 voucher.
In other words,using grabpay to pay $2000 stuff, I get $50 cashback + $55 worth of grab rides.
That's the reason why I didn't get from DynaCore but from other shops that accept grabpay. For my rig, I save $100+ using grabpay.