If your shipping rates or rules are not being calculated properly, such as the shipping rate being doubled, or multiple rates are being combined instead of triggering a shipping rule, then you might be using multiple product locations or app locations.
We have a blog article as well that goes into detail why this happens on Shopify, and describes which method might be suitable for your store using locations and when to enable single origin mode for more detail.
There are two scenarios for this:
- You are using drop-shipping apps for your inventory
- You have multiple warehouses
For scenario 1, if you are using drop-shipping apps for your inventory, you can usually change those to your store location without issue. That will fix the issue and your shipping rules should start working as you expect again. We have a drop-shipping apps multi location guide here which shows you how to fix this issue.
For scenario 2, if you have multiple warehouses and need to keep them for the inventory tracking, you can consider enabling Shopify's single origin shipping mode. Using single origin shipping allows you to keep your products in multiple locations, but shopify still sends the request as if it comes from a single location. There are some restrictions to this mode, however. For more detail on enabling single origin shipping please use our help guide to enabling single origin shipping, or we also have a blog post with the same steps and information.
Better Shipping is available on the Shopify App Store.