Just try to look back for your shopping page. I guess maybe the paypal page needs "refresh". Once you had found the page again, just check-out normally. May I know which web that you tried on your pp?
It's quite simple actually. Have you obtained the card yet?
If yes, then the next step is to
register for Maybank2U. Even though you might have register one before, but since you'll different number on your card, then you'll have to register again as the numbers on your old card is not working anymore.
After you log-in MBB2U, in your account page, please look up under
[Utilities] for
[Maybankard Secure Online Shopping Registration].
From there, key in your MBB debit card details. You'll be notify once you had it register successfully.
After you register your debit card under this secure online shopping registration, then you'll be able to link your debit card to your paypal.
Good luck in trying out these steps ya~

Hm, maybe next time, I'll checkout with Paypal. The website was drugstore.com..