I think they provide a backend so you can issue your own cards, with bank accounts routable through normal banking systems. Payoneer famously rely on third party "back-end" banks for their services, as they issue cards, offer routable bank accounts, cash withdrawal, etc.

This is an extremely niche use case of course, but it's not the first time they popped up on HN at least.

In mobile ISPs, MVNOs are quite common, and there is a large amount of customer base because they simplify KYC, sales, and customer on-boarding. Technically, this API should provide the platform to build a similar "Virtual bank". I do not think anybody without a significant technical and financial resources will be able to pull it off.

Another use case I can think of are market places like ebay, Amazon, Aliexpress, etc. Each seller receive a bank account that they get their payments deposited to, and can be withdrawn from their branded card. I do not see this being a commercially viable option for many, because pretty much every country has free or almost free systems in place to simply transfer money, and not take the unnecessary burden of issue cards, maintaining bank accounts, etc. Payoneer used to run a similar program, with branded cards, custom fee structures, etc, but it eventually failed as far as I know.