I finally have Amazon Payment setup and running up to the point that customer should be returned to my website.

But the return page is blank. The return page URL in the Admin/Modules/payment is: http://www.sourceforherbs.com/index....eckout_success

Following is in the URL line of the blank page:
/checkout_by_amazon.php?action=ResetCart&amznPmtsOrderIds=115-6882490-2544211&amznPmtsReqId=cartId%3A64059&amznPageSource=CartPage&showAmznPmtsTYPopup =1&merchName=Source%20For%20Herbs&amznPmtsYALink=https%3A%2F%2Fpayments-sandbox.amazon.com%2Fsdui%2Fsdui%2Foverview

What did I setup incorrectly?