Issue: I am trying to add a SKU to a shipping plan, but the search bar doesn't bring up any results.
Solution: The product you are trying to add is likely a kit SKU. This means that the SKU has components associated with it. Instead, add the individual components to the shipping plan with the quantities you plan to send. Kit SKUs should not be added to shipping plans; only the component SKUs.
In the below example, we see this product has 1 kit component of "KBK02." When I create a shipping plan, I need to add the SKU KBK02 instead of the main product SKU. Always add the component.