Finally someone with the same issue! I have been having this issue since early last week (US number as well). I'm unable to log in using the app due to the OTP issue, but it will let me log in using a web browser. I opened a ticket with AirAsia, and they closed it saying they "acknowledge my concern." I even chatted with AT&T, and no issues on their end. Hopefully AirAsia is able to resolve this OTP issue soon. Luckily my flights aren't until October.