Every billing mistake turns into someone else's problem
A plan change doesn't go through properly and a customer gets charged twice. Support picks up the complaint. Finance fixes it by hand. If nobody catches it in time, the customer's bank reverses the payment and you pay a fee on top.
With a few hundred customers, you can fix these one at a time. With millions, even a tiny error rate means thousands of unhappy customers every month, and a team that spends its days cleaning up after the billing system.

















