Set it up at home
Finish the SMS step while that number has service. Keep the account signed in and make sure you can unlock the phone without depending on an unfamiliar connection.
Match the cardholder details to the issuer’s records and confirm that the card appears in the account. Use your own active card rather than borrowing a companion’s details to get past a screen.
Photograph the original document clearly, with its edges and text visible. If the app gives a precise reason for rejection, correct that reason before another attempt; keep the message for support if it repeats.
If it goes wrong
Download a fix to read it without a connection.