App block Cors error calling backend

Topic summary

A developer is experiencing CORS errors when their Shopify app block attempts to fetch data from an external backend. The error indicates that the ‘Access-Control-Allow-Origin’ header is missing from the preflight response, despite the backend being configured to allow requests from https://extensions.shopifycdn.com.

Key Details:

  • The fetch call works in Postman with the correct origin header but fails in the browser
  • Using an ngrok tunnel URL for the backend
  • CORS configuration appears to be set up on the backend

Attempted Solutions:

  • One user suggested implementing a Shopify App Proxy instead of direct fetch calls
  • The original poster tried this approach but still encountered CORS errors related to preflight request redirection

Current Status:
The issue remains unresolved, with another user asking if a solution was found.

Summarized with AI on November 1. AI used: claude-sonnet-4-5-20250929.

I still seem to be getting a Cors error, something do to with the preflight not being able to be redirected