Issue with “Backup rates” message in Carrier Service API

Fulfillment & Inventory
38

@Alan_G - Following up on @Min_Liu’s related thread where Shopify confirmed the issue was caused by the outbound proxy timing out prematurely (ticket #64552215) and marked it as resolved on March 12. We experienced what appears to be the same issue 10 days later on March 22, 2026.

We’ve done an investigation on our side and can confirm the request never reached our server.

The order:

  • Shop: pipers-farm-cullompton.myshopify.com

  • Order: gid://shopify/Order/6718505418826

  • Checkout token: d7884c0a5651370360b57ba9b1cd330b

  • processed_at: 2026-03-22T19:00:14+00:00

  • Shipping line: code: "backup_rate", source: "merchant_customized_by_order_value"

  • Shopify admin shows: “Order recovered using custom (value-based) backup rate because Flare shipping did not provide a rate”

What our logs show:

  • Our carrier service responded successfully to every call Shopify made for this shop. Between 18:54 and 19:15 UTC, we handled 50+ carrier callbacks for this merchant, all returning HTTP 200 with valid rates in under 300ms.

  • For this specific customer’s checkout, we received and responded to 4 carrier callbacks between 18:54 and 18:55 - all returned valid rates with HTTP 200.

  • No further carrier callback requests were received for this customer after 18:55. The order was placed at 19:00:14.

  • Other customers on the same merchant were having their carrier callbacks processed successfully between 18:59 and 19:01 - confirming our server was healthy and reachable from Shopify’s infrastructure during the exact window.

Server health during the incident:

  • Single App Runner instance, running continuously since March 19 - no container restarts, no deployments, no scaling events

  • Verified across application logs, HTTP access logs, and Sentry performance tracing - all consistent, no request received for this checkout session

This matches the exact pattern described in this thread and in ticket #64552215 - Shopify’s outbound proxy appears to have dropped the carrier service call before it reached our server, then fell back to backup rates. Our carrier service was never given the chance to respond.

Could you confirm whether the fix from ticket #64552215 has been implemented yet? Happy to provide any additional data.