When I try to link my card this thing always show Your card has been declined. Please try a different payment method. I tried this multiple times, and my credentials in paypal and in my card are the same. I don't know how to fix this.
As you have not added your country to your profile (so we can see when we hover over your username) or said in your post which country you are in then sadly can't advise. Paypal varies a great deal country to country so you need to tell us where you are on this worldwide community forum.
Advice is voluntary. Kudos / Solution appreciated.