You can't register a card using the Joyn Business App Lite.
Your customer doesn't have a registered Joyn card? Suggest for the customer to download the Joyn app on his smartphone. Registration is easy, and your customer will always have his Joyn card handy!
Your customer doesn't have a smartphone? He can register the card using the Joyn app on your iPad or via the web page my.joyn.eu/card-registration.