Adding A Payment method

I want to add a visa to my payment method but it won’t let me.it says “Your payment method is not valid in this Store.Please enter a new payment method”

how can I fix this and add it?

also I want to remove another visa but it won’t let me it says “There is an active subscription on this account that requires at least one payment on file.” I don’t understand what do I need to do to be able to remove it?