I did some research but could not find the anster to this.
I have inventory in Amazon FBA warehouses and I am set up my listing on Shopify so that the product is linked correctly to the Amazon Fullfilment channel (shipping rates, linking the SKU, linking the fulfilment channel and tracking inventory, etc).
I have noticed that on for a product which is completely sold out (i.e. no more fullfilable inventory on Amazon) the quantity for that variation will show 0 on Shopify and on my Amazon Seller Central. However when I go to amazon.com and look at the listing, that product variation is showing up as "In Stock" and fulfilled by the seller (me).
For example for a T-Shirt, I sell sizes small/medium/large. The medium/large are sold out and on my amazon seller central inventory screen it shows there is "0" fullfillable inventory. On the Shopify listing the medium/large variation has "0" as well, however on amazon.com when I go to the listing for the t-shirt it now shows that the medium/large is in stock (however it is not fulfilled by amazon) Has anyone come accross this? I have had someone purchase the item on Amazon since it shows in stock but I don't have any fulfilable inventory.