Transaction Error: Please enter the token sent to your phone to conclude payment of XXXX

What does 'Please enter the token sent to your phone to conclude payment of XXXX' mean?

The means that the customer did not input the token sent to them by their bank to complete the transaction of XXXX amount.

What can I do about it?

They will need to retry the transaction and input the token sent to them by their bank to complete the transaction.