The reason why this or these SKUs couldn't be mapped
It seems that a few Shopify SKUs are not the same on your Amazon Seller Central account, as a result, they couldn't be mapped. By default, if they are the same on your Shopify store as well as on your Amazon Seller Central account, our app will map them automatically.
How to map:
Go to the Products Linking Page
Select an existing Amazon Marketplace from the Account drop-down menu
Select UnLinked SKUs from the Filter drop-down menu
Hit the Search button
Click on the (Update / Link) button corresponding to those Shopify SKUs, whom you want to (update / link) with an Amazon SKU
Below, is a screenshot to show you a visual representation of all the above-mentioned steps.
Enter the missing Amazon SKU in the SKU field, further hit the Submit button. Below is a screenshot to show you a visual representation of the above-mentioned step.