Detect when a carrier returns no rates for an addressable zip at checkout. Query a secondary carrier instantly for fallback rates. Send an alert to operations when both primary and backup fail. Track rate failures in a dashboard to identify service-area mismatches with carriers and prevent future gaps.
A mid-market DTC merchant using ShipEngine for multi-carrier shipping faced customer checkout abandonment when the primary carrier returned zero rates for a zip code that should have been in its service area. Without a backup mechanism or visibility into these gaps, valid orders were lost at the point of rate lookup.
Four pieces
Checkout
Rate Validation Hook
Intercepts ShipEngine rate responses during checkout and flags when a carrier returns zero rates for a zip that should be in its service area.
# Function input query — Delivery Customization
query Input {
cart {
deliveryGroups {
id
deliveryAddress {
zip
countryCode
}
deliveryOptions {
handle
title
description
}
}
}
}
Removed buyerIdentity.deliveryAddress — BuyerIdentity does not expose address fields in Delivery Customization schema. Zip and country are available from cart.deliveryGroups[].deliveryAddress only.
Shipping
Backup Rate Engine
Automatically pulls a secondary carrier's rate for the zip when the primary carrier returns nothing, allowing checkout to proceed without interruption.
Backend service + ShipEngine API calls
Operations
Dark-Zone Alert
Sends a Slack or email notification when a zip code in the merchant's approved service area returns zero rates from both primary and backup carriers.
Shopify Flow + webhook
Shopify Flow editor: When → Thenflow
Trigger: Custom webhook (backend fires when rate lookup fails for a zip)
Condition:
– Zip is in your approved service-area list (stored as app data)
– Primary carrier returned no rates
– Backup carrier also returned no rates
Action:
– Send Slack message to #shipping channel with zip, attempted carriers, timestamp
– Tag the order (if created) as 'rate-gap-alert'
– Optional: Create a Slack thread for manual override options
Backend sends the webhook; Flow routes it to Slack, email, or PagerDuty depending on urgency.
Operations
Failure Dashboard
Live view of which zip codes are hitting rate gaps, frequency, and responsible carrier—enabling merchant to contact carriers about service-area mismatches and prevent recurrence.
Admin dashboard (custom app)
Admin GraphQL explorergraphql
# Admin GraphQL — query your app's stored rate-failure logs
query RateGaps($first: Int!) {
shop {
id
name
}
orders(first: $first, query: "tag:rate-gap-alert") {
edges {
node {
id
name
shippingAddress {
zip
country
}
createdAt
metafields(namespace: "rate_gaps", first: 10) {
edges {
node {
key
value
}
}
}
}
}
}
}
Removed appInstallation (not exposed on Shop). Moved metafield query to orders themselves—each order can carry its own rate-gap context via metafields, which is the real pattern for per-order failure tracking.
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