If the Product not found (product_not_found) warning message appears when importing an order, the reason is that the SKU for the product sold on Amazon was not found on your website.
To overcome this you can follow this procedure:

• open the Prestashop product and click on Modules -> AmazonSync tab
• make sure the marketplace you are trying to import the order from is selected within the menu at the top of the page
• fill in the ASIN for your product or combination within the dedicated field
• enter the Order’s tab inside of the AmazonSync module
• enable the Prioritize ASIN code option and save
• try to re-import the order by choosing to show the orders with errors in the dedicated menu

The ASIN that you have to fill in within the product sheet can be gathered from your orders summary on Amazon, see the following image for reference.