If it is cash based accounting, revenue and expenses are booked when the money changes hands.

If it is accrual-based acocunting, it takes place when the event legal triggering the change of ownership of goods in the transaction takes place, which depends on the shipping terms, which could be anywhere from when it is available for the buyer’s transport agent to pick up at the seller’s facility (EXW) to when it is delivered, unloaded, and at the buyers door (DDP) or any of a variety of places in between (FOB Origin, FOB Destination, and a bunch of other potential shipping terms with their own rules on when ownership—and responsibility—transfer from seller to buyer.)