Cannot process payment to buy Costco JP only accepts Mastercard. When purchasing through this app or website, it bounces back with a 3D authentication error, which means the OTP wasn’t received or processed. The OTP is processed (through your card company) and you should be able to receive it, the problem is within Costco website backend.
This app is pretty much trash and a gateway of the existing website, which is garbage by itself. There is no customer service to talk to. IIRC, this problem had always been here for a few years, probably started in 2022. I recall being able to order online easily back in 2021 during COVID season.