The card is advertised to work in so many countries. Was denied for transactions in Qatar and United Kingdom, so far. Tried two failed two. More to go!
As the program is in beta stage, there may be some hiccups at the moment. Try going into card settings and then locking and unlocking it, disabling international transactions and enabling them again.
If the issue still persists, raise an issue in the app support centre and someone would be able to help you out.