Hello @NamNguyen!
Sorry to hear you are experiencing the same issue! I know how important it is to be able to pay your bill with your MyAT&T app!
If you are abroad currently, I highly recommend connecting to Wi-Fi, uninstalling and re-installing the MyAT&T app. If you are still having issues making a payment, try accessing your account by clicking here. Click on “View” for guidance on making the payment.
In addition to the above steps, you can give us a call toll free at +1-314-925-6925 to pay while traveling! Please let me know if you need any additional help!
Jonathan, AT&T Community Specialist