It didn't work for me adding a US card.  Grab gives an error saying the credit card needs to support OTP security, which of course US credit cards do.  So after a few emails with Grab support, they finally explained that US cards use "3D Secure version 2, while here in TH it's is still on version 1" or something to that end....  I tried adding 3 different cards, none worked.  Anyone had better luck?

 

When I first started using Grab a few years ago, I had no problem adding a US card.  So this is a recent development. 

I have the same problem with True. I used to pay online with my card but now comes back error. I read that the 3D Secure V2 is supposed to step back to V1 but that has to do with the setup of the company server. I guess Thailand just isn't making the effort.