On Account

When you tell the bartender to set up a tab, you don't pay for every drink a la carte. Instead, at the end of the evening, the barkeep gives you a check for $172 which covers, well, everything. All of it was put on account for the evening.

And the real world works much this same way, especially when known companies buy things regularly from the same suppliers. Only they don't tip 20% for good service and ears that listen.