I think melvinram are dmpayton are both right. The entrepreneur only knows there is actual demand for his product when someone pays or makes a promise to pay for it.

But logically the product still comes first. The entrepreneur might take a pre-order on a product that's not available yet, but it must exist at least notionally.

Say you want to buy a kg of rice from me. You might buy it on the spot for $5. You might pre-order and pay me $3 now, and I promise to deliver it in December. You might pre-order and promise to pay me $5 in December, when I'll deliver it (a forward contract). I might deliver it now and you promise to pay me $6 next month. All those transactions are essentially the same, only the settlement details (and risk, etc) change.

In all those cases the existence of the product, or at least an expectation that a specific product will be available sometime, is a pre-condition for the transaction.