Did not knnow express business accounts had to be verified before it would work. I was getting this error:

"We are sorry for the inconvenience. The PayPal account authentication settings are not yet set up, or the API security information is incorrect. We are unable to complete your transaction. Please notify the store owner so they can correct this problem. (10002)".

Also, be sure that if you have entered your API info like I did, after verifying get another API...

Hope this helps someone...