What do I do when I need to back out of a ebay sell ?

I recently placed an item on ebay for sell and it was bought , the buyer paid the money and its now in my bank account (whole transaction Through paypal) but i can no longer ship and sell the item anymore, but i already have the buyers money , is they're a law on ebay against this ? can i back out of a sell ? and now that i cant sell the item anymore what do i need to do ?