An SKU helps in stockkeeping and tracking individual items. If you want to have an accurate inventory management system, one of the most important things is to set up SKUs for your products. 

When you create an item, make sure to enter its SKU and mark it as active. If the SKU is missing, the item will not appear in the app under the SKU Mapping page. When an order is created with a blank SKU, it will process in Shopify but will not sync to Amazon. In the Order Log page, the status will display as “REJECTED BY AMAZON.”

NOTE: Your product SKUs must match between Shopify and Amazon (not the ASIN or UPC). Amazon only accepts the SKU from us, so it must match exactly.

Check the screenshot below for an example of such an order in our app.