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Shopify’s Delivery Customization API can rename, reorder, or hide delivery options that checkout already has. It cannot calculate or add a new shipping rate. For real-time calculated rates, use Shopify’s CarrierService mechanism, which sends checkout details to an external callback and displays the rates the callback returns.
Why Delivery Customization cannot calculate a rate
Shopify defines Delivery Customization as a way to transform delivery options available to customers during checkout. Its cart.delivery-options.transform.run target returns operations to apply to those options; it does not call a rate calculator or create new rates. See Shopify’s Delivery Customization Function API.
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That distinction is the key to diagnosing the issue: if a rate is missing because it was never supplied to checkout, a customization function has nothing to add. If the rate already exists and you need to change its visibility, order, or presentation, Delivery Customization is the relevant tool.
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Which Shopify API fits the job?
| Need | Delivery Customization | CarrierService |
|---|---|---|
| Primary responsibility | Rename, sort, or hide options already available at checkout. | Obtain real-time calculated rates from an external system. |
| How it works | The function receives delivery options and returns transformation operations. | Shopify sends checkout details to a callback URL, then displays the rates returned by that callback. |
| Setup focus | Configure the Function and request the option fields it needs. | Meet store and permission requirements, associate the service with relevant fulfillment locations, and operate a working callback. |
Shopify documents CarrierService as its route for real-time shipping rates. A CarrierService is connected to an external rate-calculation system through a callback URL. See the CarrierService reference.
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How to troubleshoot a missing calculated rate
- Match the implementation to the requirement. Use Delivery Customization only when changing options Shopify or another integration has already supplied. For a newly calculated or conditional rate, configure a CarrierService or a shipping integration that supplies calculated rates.
- Check service eligibility and permission. Shopify requires the
write_shippingpermission to create a CarrierService. The store must be on Advanced Shopify or higher, have a Shopify plan with yearly billing or the carrier-calculated feature added for a monthly fee, or be a development store. Shopify notes that a plan change that removes eligibility deactivates the store’s association with the service. The applicable plan terms can vary, so verify the store’s current eligibility in Shopify’s CarrierService documentation. - Verify the service is active and linked to the fulfillment location. Shopify’s DeliveryCarrierServiceAndLocations reference describes the service-location pairing used for real-time rate calculations. Confirm that the relevant delivery group is fulfilled from a location associated with the service.
- Inspect callback requests and responses. Confirm the callback endpoint is reachable, processes the checkout details, and returns rates applicable to the cart and destination. Shopify’s documented read timeout varies with the app’s request volume: 10 seconds below 1,500 requests per minute, 5 seconds from 1,500 to 3,000, and 3 seconds above 3,000. These are Shopify’s stated thresholds; the cited documentation does not assign them a publication year. See the CarrierService reference.
- Allow for cached responses when testing. Shopify says successful rate responses are cached for 15 minutes and errors for 30 seconds. Identical requests can be served from cache based on details including variant IDs and quantities, box dimensions and weight, carrier service ID, origin and destination addresses, item weights, and signatures. A repeated checkout attempt may therefore not produce a fresh callback immediately. See the CarrierService reference.
- Check the customization’s input and rename behavior. A Delivery Customization can use only fields requested in its input query. Shopify’s tutorial also notes that when a delivery option is renamed, the carrier name is automatically prepended to the title and cannot be removed or changed through this API. These are customization limits, not a way to calculate a rate. See Shopify’s delivery options Function tutorial.
Conditional rates based on a delivery date
If checkout should show a newly calculated rate only after a customer selects a delivery date, the rate still needs to come from a CarrierService or another calculated-rate integration. Shopify Community’s December 3, 2024 discussion describes passing the selected date in cart data so the CarrierService callback can use it when calculating rates: “Add shipping rate to checkout page only when user selects a delivery date”. Treat this as an implementation example; Shopify’s official CarrierService documentation is the primary reference for the API’s role.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.What to collect for a store-specific diagnosis
The API distinction explains why Delivery Customization cannot add a rate, but it does not identify the cause of a particular store’s missing rate. Gather these details to distinguish an API mismatch from a setup or callback problem:
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- USB Cable Connectivity: This printer ensures seamless USB connectivity with macOS, Windows (7 and above), ChromeOS, and Linux. KNAON printer features a built-in USB drive preloaded with drivers and tutorial videos for a fast and hassle-free setup. For ChromeOS, need to install 'FlashLabel' extension to your Google Chrome.
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- Seamless Multi-Platform Compatibility: This Bluetooth shipping label printer works effortlessly with all major platforms, including Amazon, eBay, Shopify, USPS, UPS, Etsy, PayPal, Poshmark, DHL, and more, ensuring smooth and efficient label printing. (Note: Save the logistics label as a PDF file on the shipping platforms, then import it into the 'FlashLabel Pro' app for printing).
- Portable & Stylish Design: KNAON multi-function thermal label printer offers user-friendly operation in a compact design. Its perfect size (7.17 x 3.9 x 3.43 inches) makes it simple to store anywhere. With a fast printing speed of up to 180 mm/s and support for paper widths from 1.5 to 4.2 inches. The package also includes 10 test printing papers to get you started right away.
- Store plan and whether it currently qualifies for CarrierService.
- CarrierService active state and the fulfillment locations associated with it.
- Callback URL, recent request logs, request duration, and response body.
- Cart contents and destination used in the failing checkout.
- Whether the request could be receiving a cached success or error response.
Shopify permits up to 25 active Delivery Customization Functions on a store, according to its Delivery Customization Function API. That limit is separate from the ability to calculate rates: adding another customization function will not supply a rate that the checkout has not received.
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Rongta Bluetooth Shipping Label Printer, Wireless 4x6 Thermal Label Printer for Shipping Packages, Support Phones, Compatible with Windows macOS Android iOS for Small Business
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- Good Helper for Cost Saving: Advanced thermal direct technology is adopted to achieve the printing speed of 150 mm/s, up to 72 sheets 4x6 labels/min. High speed brings high efficiency and helps your business grow faster! 203 DPI makes printing clearer. No ink, no toner, only thermal labels needed. Both fanfold labels and roll labels could be used. Label size: labels width ranges from 1.54" to 4.1"(40-104 mm), such as 4x6, 3x2, 3x1, 2x1 thermal labels and so on
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