Someone bought my item by clicking buy now but haven't paid what do i do?
You don't mention how long ago they bought it.
You can open an unpaid item dispute after 4 days.
How long ago did they buy it.
If you didn't have 'immediate payment required' set on the BIN they have four days to pay after which you can open a INR case in the resolution centre this gives them a further four days to pay.
If still no payment close the case and give them a strike and get your FVF's back.