Paypal Payments Pro on Sandbox return always #10001 "Internal Error"

Question

I've been testing Paypal Payments Pro for a while. Switching to Sandbox I got always the error number #10001 "Internal Error".

Paypal KB is not very clear about this error and many have this issue while testing in Sandbox. Someone says that Sandbox env is not 100% reliable, and keeps creating fake Pro accounts until they find the one that actually works.

Answer 1

The answer is that, following this guide, I have to use one of the default CC Numbers, instead of a fake one (even though you generate CC Number through Paypal Sandbox Environment).

It took me a while to get thorought it.