if the contract your client signed said net-30 then wouldn't a 90 day payment incur 60 days of late fees and another invoice? i feel like you could rinse/repeat that forever. It would be like a subscription to late fees.
It's absurd, that's why I like working with smaller companies.
It’s a lot of effort to keep going so it may just be more hassle than it’s worth. On the other hand, nothing wrong with that process if you’re within the terms of the contract. When the number gets large enough it will get escalated and, when you show your work, get paid and the payment clerk will get their hand slapped.
They know I don't have a choice to turn down that work just because I don't like the 90 day rule, and they only have that rule so they can keep money in their bank account longer.
And when I was on the corporate side, the vendor specifically would not do the work for me because they didn't agree to the 90 day terms, so I had to fight with my own people to get them paid faster so I could work with them.
It's just a pain all around.