Why is Simple Bundles not working with my shipping integration?
If you find that your bundles cannot be shipped through Shopify's checkout or is not working with your third-party shipping integration, make sure you have weights associated with your bundles in Shopify and your integration.
You can set your bundle weight to be the approximate weight of all the contents in your bundle.
Below is an error message that you might encounter at checkout.
To add a weight to your bundle product, go to your Shopify admin > select Products > select your bundle product > scroll to the Shipping section.