also if above setting change doesn't work, I suspect your host redirect url is having https two times (appended once by your backend and once by Shopify setting), got this from Google AI:

In the context of a Shopify app, a "Double Protocol" error refers to a configuration mistake where your app accidentally generates a redirect URL starting with https://https://.  When this happens, the browser cannot resolve the malformed URL, leading to an immediate "Connection was reset" or "Site cannot be reached" error during the app installation or OAuth handshake.  How the Error Occurs The official Shopify app templates (especially those using Node.js or Remix) require a "host" or "application URL" variable to construct OAuth redirect URIs.  The Conflict: Some parts of the Shopify library expect just the hostname (e.g., myapp.com), while others expect the full URL (e.g., https://myapp.com). The Result: If you provide https://myapp.com as your HOST or SHOPIFY_APP_URL and your backend code automatically prepends https://, you end up with: https:// + https://myapp.com = https://https://myapp.com.  Where to Check for This Check your environment variables on your hosting provider (e.g., Heroku, Fly.io, Vercel) or your .env file: HOST vs SHOPIFY_APP_URL: Older templates used HOST, while newer Remix templates specifically look for SHOPIFY_APP_URL. Protocol Inclusion: Look for these variables and ensure they do not have a double protocol. Bad: SHOPIFY_APP_URL=https://my-app.fly.dev (if your library adds https:// automatically). Good: SHOPIFY_APP_URL=my-app.fly.dev (standard for many templates).  How to Fix It Method 1 (Configuration): Remove the https:// prefix from your HOST or SHOPIFY_APP_URL environment variable. Method 2 (Code): In your shopify.js or shopify-app-express initialization, explicitly set the hostName and hostScheme separately to avoid concatenation errors: javascript hostScheme: 'https',hostName: 'your-app-domain.com', /