I work at a B2B telecom consultancy. I'm not the one auditing the bills, but every month I watch how it's done: open the invoice PDF, check every line against the signed contract, compare it with what the account used in earlier cycles, and write up whatever doesn't add up. It's slow, it doesn't scale, and it's the first task dropped when the month gets busy — which is exactly when the money leaks. And outside a consultancy it's worse: most companies just pay the bill because it arrived....