Note: To fulfill orders via FBA, the order must contain an SKU and it should be an Active SKU on Amazon. 

Let's say you receive an order in your store, however, the SKU is blank, or forgot to ad itd, you need to perform the below steps to update the SKU for the existing orders.

Step 1

Add the SKU in the Shopify product edit section. Goto Shopify Admin >> Products >> Edit product >> Add SKU >> Save. Check the below image as an example:



Step 2

Go to the Shopify order section and click on the order for which you want to update the SKU >> Click on the Edit visible in the top right corner >> Remove the item >> Add the same product with quantity(Same as the previous order)  >> Click on Update order. Now the order will be visible with an updated SKU. Check the below image as an example:


Step 3

To update the edited order data simply click on the sync/refresh icon next to Order ID. Check the below image

Once you complete all the above steps click on the Ship with FBA button and then the app will fulfill the order.