Here is where I am:

I made all changes to date fix and spiders.txt. If I use amazon shipping all is fine. Order shows up in zen cart admin and everthing is good. If I enable shipping and tax calculations after enabling call backs I get the following error in seller central:

The OrderCalculationsResponse could not be validated. Details: The XML could not be validated against the schema [cvc-complex-type.2.4.b: The content of element 'ShippingMethod' is not complete. One of '{"http://payments.amazon.com/checkout/2009-05-15/":ShippingMethodId}' is expected.].

Of course when checking out I get the We are sorry but were having problems retreving order details from the merchant.

My setting for callbacks:

Enable callbacks - true
Callback page - http://www.XXX.com/checkout_by_amazon.php
I am in sandbox so I am not using https as recommended, this also matches the address used in seller central piplene for both Merchant and Intergrator URLs. Not sure if both are supposed to be the same. Also I changed the listed domain in this post, its not xxx.

Enable Shipping callbacks - true

Enable tax calculations - true

Is shipping taxed - true , it is in GA

I have all by zone shipping set up in Zen and want to use it. Same with taxes. My shipping is flat rate based on the number of items shipped. One for all of USA, and then a zone 2 and 3 for international. Example of shipping: 1-3 items in USA is 4.50 4-8 items USA 8.75 and so on.

Any help would be great please