[jddj]

Really?

A lot (most?) of the fintechs in the UK/EU seem to use TransferWise under the covers for their foreign currency exchange, and while I haven't used the api itself yet I have skimmed the docs for it and they seem detailed enough.

They (intentionally, afaict) don't provide a checkout flow, but there's still a lot there.

[toptal]

For doing payroll like transfers, especially with strong compliance, there's a lot of under the hood functionality required. Payoneer has spent over a decade creating this, while TransferWise still has a long ways to go.