There are two possible scenarios:
1. if 'Sync Amazon orders for not-linked products' setting is not enabled- The order is marked as failed and listed as failed order in the order grid.
2. if 'Sync Amazon orders for not-linked products' setting is enabled - The order is created without a Shopify product.
How to fix this?
Case1) Due to insufficient stock
If a product has insufficient stock in Shopify to fulfill the Amazon order, please check the overview section & see failed order details. The app can not create orders in Shopify due to insufficient stock. Kindly provide the stock in Shopify, the app will sync the order with Shopify.
Case2) Due to the unavailability of SKU in Shopify
If the product SKU is not available in Shopify, the app won’t be able to create those orders in Shopify. Create a new SKU in Shopify, and link it with the app.
Case3) Due to a glitch in the server
Sometimes there are technical issues that can hamper the order syncing. In case you spot such an error, filter out Orders by selecting “Failed Orders” in the Order Grid. Click on “resolve” and then click on Create Order on Shopify.