I assume you sold something on eBay. You have no obligation to ship the item until payment is received.
You may also file a non-paying bidder alert, in which eBay inserts itself into the process to attempt to gain you payment. There is a process for you to follow.
eBay cannot make the buyer pay. But, it can impose an alert to warn other sellers, and can also suspend the buyer's account.
You may leave neutral or negative feedback.
If the buyer hasn't paid by the time imposed by eBay, you can file for a final value fee credit so you are stuck with the listing fees but not the final value fees.
If we're not talking eBay here I'm afraid I haven't a clue.