How to add my debit card?

If you're talking about Apple Pay, check if your country supports Apple Pay AND if your card issuer is among the partecipating banks in this list:--> Countries and regions that support Apple Pay - Apple Support

Should be this case, set up your Apple Pay, using these instructions:--> Set up Apple Pay - Apple Support

Regards

Giulio

You can find instructions here. Please let us know if you have problems doing so.

Add a payment method to your Apple ID - Apple Support