Carriers occasionally respond with HTTP 3xx redirects or 4xx client errors. Previously, this left merchants without shipping options at checkout. The rate service now extends its existing error-handling path to treat these responses as recoverable failures. This change triggers a fallback to backup rates instead of resulting in a hard failure. As a result, shoppers still see viable shipping methods, safeguarding conversion and improving overall checkout reliability.
This is a companion discussion topic for the original entry at https://shopify.dev/changelog/shipping-rates-return-backup-rates-for-3xx-and-4xx-carrier-responses