This was a painful learning for me when I worked for a megacorp: the bigger the customer, the less likely to pay on time.

For me as an engineering manager at the “big customer” it was a constant embarrassment. We worked with small scrappy vendors who I was on a first-name basis with. Megacorp would just never cut the checks. They would negotiate super aggressive terms to start with and then still intentionally not meet the agreed terms. I had close collaborators telling me they really needed the $$ to meet their own bills and all I could say was “I’ll send another email to purchasing and hope for the best!” Hated that so much.