I removed the plug-in for downloading digital goods and I have added manually a PayPal button. Evreything is working fine now. Thank you for your immediate response.
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I get the following error, after pressing the Paypal button: Error - Double check your Business API settings. SetExpressCheckout API call failed. Detailed Error Message: You are not signed up to accept payment for digitally delivered goods. Short Error Message: Transaction refused because of an invalid argument. See additional error messages for details. Error Code: 10004 Error Severity Code: Error The same button works OK in sandbox mode.
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