In this example, a product has the wrong Fulfillment Service in Shopify settings.
In order to change the "Fulfilled by: X" box shown below to manual fulfillment, you will need to log in to your Shopify store and update a setting in your product variants.
Update settings within your Shopify store
Click on Products on the right-hand column.
Click Active to show only your active products.
Then, click on a product.
Scroll to the Variants section. There, you can Edit each Product Variant.
Scroll down to the Inventory section. Choose Shopify from the dropdown and click Save in the top right corner of the screen.
Once this is completed, you will be able to manually import your Items into Whiplash.