Well, first Amazon said it was a SSL problem. It wasn't, Amazon's ipn checker was returning a incorrect response. Then they said it was a redirection problem, but we got that sorted out and nothing was fixed. I explained to Amazon that the payment part works, just not the login and they are checking on that from their end. Meanwhile SiteGround was able to see an error message that didn't show up on any of my logs. It was a 503 Error with message - header does not contain x-amz-sns-message-type header. I contacted patworx with that information and they are looking into it. I don't think it is a TB specific issue because I have the same problem on the prestashop site. But I have two different versions of the Amazon module, one for 1.7 and the other for 1.6. I disabled it on both sites for the time being. It is the free Payments Advanced by patworx.