I had the same with some UK and EU cards...

The security/fraud dept at Lloyds Banking Group (UK) gave this explanation
- the issue is due to the way that Grab verifies the card when first adding it
- whether your card works will depend on the card provider's anti-fraud measures
- Grab as a merchant isn't blocked, but the method they use to verify cards is apparently used by scammers to verify if stolen card details are valid, hence not being allowed by some card issuers
- cards from LBG (MBNA, Lloyds Bank, Halifax, Bank of Scotland etc) will not work with Grab for this reason

Other EU/UK/PH cards that I have tried worked ok eg BPI, BDO, GCash, Maya, Revolut, Curve, Chase, Monese, Wise
(I haven't tried any cards that have foreign spending fees)

Just keep trying cards until you find one that adds successfully
- if you can actually add it to the app then you should be OK