It's always interesting to me how easily corruption occurs. I always assume that accounting double checks things and so on, but I've seen so many business where someone just creates an account and money goes out and ... nobody notices for years.
I've even created automated invoices for some companies and realized that some data was missing for months. And yet they got paid significant amounts. I realized that the invoices could have been for just about anything and they would have gotten paid ...
There's an excellent book on the subject by Dan Davies: https://www.inkwellmanagement.com/books/lying-for-money
The larger the usual bills, the larger the rounding-error-level amounts. I've had some fun time with a vendor recently where they just forgot to bill a few $k for months, but remembered when asked for quota increase.
When Robert McNamara took over Ford, accounting was so messed up, they would weigh their invoices and if the amount wasn't too far off from the expected dollars/pound ratio, they would pay it.