Dynamically Adjust Shipping Rates by Postcode on Shopify Plus Checkout

Shopify Plus
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Topic summary

A developer is building a Shopify Plus extension to dynamically adjust shipping fees based on customer delivery postcodes using a client-provided postcode-to-rate mapping.

Key Challenge:

  • Seeking guidance on which Checkout UI extension type or API enables dynamic shipping rate adjustments at checkout
  • Has observed third-party apps offering this functionality but cannot locate appropriate API endpoints

Current Status:

  • Assumes custom development can replicate paid app features but needs technical direction
  • No responses or solutions provided yet; question remains open
Summarized with AI on October 28. AI used: claude-sonnet-4-5-20250929.
1

I’m about to build a Shopify Plus extension that applies shipping fees based on the customer’s delivery postcode. My client has provided a complete list of postcode-to-shipping-rate mappings. Which type of Checkout UI extension or API would allow me to adjust the shipping fee dynamically at checkout?

I’ve also seen paid third-party apps offering similar functionality. I assumed that we can develop whataver function that provided by third party app but I haven’t found any exposed API endpoints that fit my requirements.

Please advice. Thanks!