US cards, ahh that is a complex matter 😄
Many companies here actually like to block US cards, because 1), they usually lack 3DS/ACS enrollment, that means, no OTP, and 2) they are often rejected because since there is no 3DS involved, processors and merchants here dont want the liability passed to them, they prefer 3DS transactions because they are not liable for fraud, and 3) US cards get a much higher rates here than local cards (imposed by local acquirers for a good reason). so for example, 1.25% fee on international cards, but as low as 0.4% for local cards. if they are not making much profit, by allowing US cards are likely to be at a loss.
you can use your US card here as long as the app uses a decent payment gateway, that has PCI-DSS. the most popular in Thailand is 2C2P, and then Omise/OPN next to be the most secure, anything else dont trust.
I work in this field, just can't share more than that I already did.