On direct retail sales, payment is usually at the same time the order is fulfilled. On sales to distributors, say CDPR to GOG or Steam, the traditions of commercial credit apply. Which is to say, you send an invoice marked "NET 10" or "1% 10 NET 30", and the distributor ignores it and actually pays up when your accounts receivable clerk sweet-talks or threatens them into paying. An A/R clerk who knows how to treat each customer so that they pay reasonably close to on time and still remain an eager customer is an indispensable asset in any business.
It still works that way when digital goods are sold. Some artifact, like a key, is transferred; it represents the right to sell a copy if you're a distributor, or use a copy if you're an end user. The fact that these keys are bits in an E-mail doesn't change the tradition: you pay up front, everybody else in the pipeline gets credit. For the number of keys you received.
Preorders invoke the single greatest contribution of Italy to world commerce: double-entry bookkeeping. A refundable preorder creates an asset (the money you paid) and a liability (the right you have to get it back). It becomes income when they ship and you can no longer cancel.
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