Custom Shipping API for Multi-Recipient Orders on Shopify

Integrate a custom shipping date and rate provider with Send To Many for delivery date selection on multi-address Shopify orders.

Requirements

• Any paid Annual plan in Send To Many, or the monthly Growth tier or higher
• Development resources to add one or two new API endpoints to an existing custom shipping or delivery app
• Understanding of Send To Many's Date and Rate API

Many gifting merchants have complex date and availability requirements for specific products, locations, and time periods. Some are able to use third party apps such as Zapiet or Bird to power this functionality in their Shopify checkout experience. For those merchants, Send To Many can integrate directly with those apps to offer the same options in multi-recipient checkout that they already offer in the standard Shopify single-address checkout.

Other merchants have developed custom apps to support their specific shipping-date and shipping-rate logic. Send To Many's Date and Rate API makes it possible for merchants to adapt their existing functionality to the multi-recipient checkout experience.

Many merchants rely on custom apps to control:

• Which delivery or ship dates are available
• Which shipping rates apply for a given address, product mix, and date

Those apps may be implemented either:

• As Shopify Carrier Services (returning rates directly to Shopify), or
• As Checkout Functions / Extensions with custom logic that is not exposed through Shopify's rate-request flow

Send To Many's Dates and Rates API endpoints let those existing apps power multi-recipient checkout and bulk order uploads without re-implementing their logic.

Here is how the date and rate selection process works in Send To Many. For each recipient:

• Send To Many asks the merchant's app which dates are valid based on the address and products set for each recipient
• Shows only those dates in a picker
• Then determines the available shipping rates for the selected date
• Defaults to the first returned rate, while allowing the buyer to change it
• Includes the selected date and shipping rate on each resulting child order

Technical Overview: Two Integration Patterns

Merchants only need to implement the pieces that match how their shipping app already works.

Pattern 1: Date-Aware Rates via Shopify Carrier Services

Best fit for: Custom shipping apps that already accept a shipping date selection and return valid rates through Shopify's Carrier Services API, where rate logic can account for address, products, and selected ship or delivery date.

How Send To Many integrates:

1. Delivery Availability endpoint

   • Send To Many calls the Delivery Availability endpoint with the recipient address and selected products.
   • The app returns which dates are allowed or blocked, or an error message if no dates are available. It can also return optional custom order properties (tags, notes, line item attributes, etc.).
   • Send To Many uses this response to render a constrained date picker.

2. Shipping rates

   • After a date is selected, Send To Many requests rates from Shopify.
   • Shopify calls the merchant's Carrier Service, which returns date-aware rates.
   • Send To Many displays the rates exactly as Shopify returns them.

This pattern allows merchants to reuse their existing Shopify rate infrastructure, with the addition of a single endpoint exposed to Send To Many.

Pattern 2: Rates Calculated Outside Shopify Checkout Functions

Best fit for: Shipping apps implemented using Checkout Functions or other custom logic where valid dates can be calculated independently but shipping rates cannot be returned through Shopify's Carrier Services API.

How Send To Many integrates:

1. Delivery Availability endpoint

   • Send To Many requests valid delivery dates using the same inputs: address and products.
   • The app returns date picker configuration and optional order properties.

2. Shipping Rates endpoint

   • Once a delivery date is selected, Send To Many calls the Shipping Rates endpoint.
   • The request includes the address, products, and selected delivery date.
   • The app returns a list of valid rates for that specific date.

3. Rate selection

   • Send To Many displays the returned rates in order.
   • Defaults to the first rate.
   • Allows the buyer to change the selection.

This pattern gives merchants full control over date-specific pricing logic without relying on Shopify's rate-request pipeline.

Contact us to explore your custom date and rate integration.