Sorry, I did not receive the answers. I use the official package named boto https://aws.amazon.com/de/sdk-for-python/
You need a developer account which will be authorized from a seller account to use the API on behalf of them.
The third party involved is the german Afterbuy https://www.afterbuy.de/. There you can mark a sale which is fulfilled by the seller as sent and upload an invoice. The sales fullfiled by Amazon are automatically marked as sent and you only need to upload an invoice. Since now I only import the sales to tryton and mark them as sent and paid by requesting the amazon API - so in Tryton I have more or less a mirror of the Amazon transactions.
To have a full working module we must also implement the cancellation, retour, partially sent and other stuff.
For products we should implement an other module (product_sale). In real live selling on amazon is not only uploading a product. The seller are using different names and descriptions. Sometimes they are bundling products which have different templates in tryton to one in amazon.
Stock management I have done by routing AFN (amazon fulfillment) to an ‘virtual’ warehouse and MFN (merchant fulfillment) to a real warehouse of the company. But this in reality is more sophisticated since there are different warehouses for special markets on amazon.