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Your mobile must have internet access. NFC connection, the technology that enables the transmission of data (in this case, the transport tickets you buy and load onto the card), must also be activated at a very short distance. You can check this in the "Settings" section of your mobile.
Tap the app icon on your mobile. If you haven't downloaded it yet, you can do so from here: transport-card-app
To make a top-up, you must first register your bank card. After topping up, you can remove the bank card from the application.
Check your balance and/or load your transport ticket.