Members can have up to a dozen 'gift' addresses on their PP accounts. The name indicates why.
All the addresses have to be in the same country.
Don't panic.
Tell the buyer the date and service of the shipment. If you have a Delivery Confirmation number, give it.
Now stop.
If you don't have a Delivery Confirmation number (sometimes inaccurately called tracking), then be aware that you will lose an Item Not Recieved Dispute.
So you want to make sure the buyer doesn't go that route.
Calmly and politely, give the date and service again, and give the address that you shipped to.
Then stop.
If the buyer tells you he has moved, tell him, calmly and politely, to check with the new tenant and with the post office that services his old address.
Tell him, calmly and politely, that if he filed a Change of Address with the PO when he moved, that the shipment may have a slight delay but that it will reach him.
He has up to 45 days to file an Item Not Recieved dispute.
If he moved without leaving a forwarding address, the shipment will eventually be returned to you.
If he has moved without leaving a forwarding address, and more than 20 days have passed, refund him. This is especially true if you don't have a DC number to prove he has received it.
The money is less important than your feedbacka and DSRs. It is much less important than losing a PP dispute, which goes on your seller account.
It's not fair. But it is just business.