Why I can’t purshache in Apple store?

What country are you in? What country is your card from?

What country's store did you try to use?

The itunes store is country specific. If you tried to use the U.S. Store, it would require a U.S. payment method with a U.S. Billing address for example.

I believe Puerto Rico has its own iTunes store that is different to the U.S. store.

The Puerto Rican Card may work in physical stores, but not in the iTunes Store.

You would need to use an American Card if you want to use the U.S. store.

You can contact iTunes Support directly and see what they say:

iTunes Store - Contact Us - Apple Support