In order to transfer or synch your cards on another device you need to register an account. Tap on the "cog icon" in the top left corner of the screen, then to "account" and pick the account-type of your choice: mobile-pocket account with e-mail address or use your Facebook, Google or Apple log-in credentials.
Then log into mobile-pocket on the second device with the same account-type and the same credentials.
Then log into mobile-pocket on the second device with the same account-type and the same credentials.