Ok, apparently this is the situation: “To accept payments using the new REST APIs and PayPal Mobile SDK, we currently require a U.S. PayPal Business account. But stay tuned for more country support. Note that most countries can use our Classic APIs.
This is the reported problem: “Note: Direct credit card processing is not available for you when using REST APIs. Your live credentials are inoperable for direct credit card processing for your country but your test credentials are enabled for sandbox testing.”
So, the question is how to use classic API’s with Express Checkout? Or any other solution would be much appreciated.