Does the item exist in Whiplash, and does the variant ID match? Find your Variant ID.

In Shopify, was the product's variant set to be fulfilled by Whiplash before the order was placed? If set to "manual", please verify your shop's settings to import variants are also set to "manual"

In Shopify, was the product's variant set to "require shipping" before the order was placed?

In Shopify, was the item marked as fulfilled before being shipped by Whiplash? A Shopify preference may be causing this to happen automatically. In Shopify, go to Settings→Checkout and find "After an Order has been paid"