The sandbox they provide is even worse in terms of response times.

And lacks documentation. Or the documentation that is there is wrong. Or it's there but missing fundamental details. Or it's right but you question how it could possibly be a good design decision.

Or the documentation that describes something like it works in the sandbox, but not in the production system or vice versa. Developing for Paypal is a lot of fun.

Oh, please. I think a lot of their core backend is still in C++ so maybe we should blame C++ for the slow API?

Heck, Bitcoin, a decentralised peer-to-peer "currency", feels faster. Even if it takes ten minutes to confirm a transaction, and longer to be certain.

Reasonably certain based on what evidence ? Because its API is slow ?