The final value fee is the fee eBay charges once an item is sold. It will be a percentage of the final amount that the item sell for. Usually just a couple of dollars unless you sell something really expensive. I don't know why they are returning you that money.
Maybe they are running a deal where you would have some credits in your account so the next time you sell something then they will not charge you the final value fee.
It will just be returned to your Paypal account or will stay in eBay as a credit in your account.
What will be returned? And what do you do with credits on there?