It often makes sense to give buyers a lower price in return for paying you in advance. However, that doesn’t mean you have to give them a discount from your regular price.
Instead, reposition your regular price as your payment-in-advance price. Then charge a higher price to buyers who pay you at the time of delivery or performance. This becomes your new regular price.
This way you’ll give buyers an incentive to pay you sooner without killing your profit margin. And your buyers will be happy because they can still get a price discount by paying in advance.