PayPal Express eTransaction has status "in Process" or paying an order with PayPal Express and performing redirect to external system fails in an error:
Your payment failed. Please contact Provider.
The following error can be found in BA logs ( PAYPAL_EXPRESS.log for pre 6.0 or generic_worker.log in BA 6.x ):
"Merchant not enabled for reference transactions"
PayPal live account misconfiguration.
Please contact PayPal Support, more information can be found here.