Have you encountered a CORS policy error while trying to call an external API with Webflow Logic? It works fine in the designer, but raises an error when deployed. Any suggestions or solutions for this issue?

CORS policy errors often occur when using Webflow Logic to call external APIs from a deployed site because browser security restricts cross-origin requests that don’t include proper headers from the API server.

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1. Understand Why It Works in the Designer

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• Webflow Designer uses Webflow’s own infrastructure to run Logic workflows, which can bypass typical browser-based CORS restrictions.
• Once deployed, the same call is made client-side from your live domain, where CORS policies apply strictly, and errors are triggered if the API server doesn't allow your origin.

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2. Check API CORS Headers

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• Make sure the API you’re calling includes the Access-Control-Allow-Origin header allowing either:
• A wildcard (*) if public access is acceptable.
• Your Webflow domain, e.g., https://your-site.webflow.io or your custom domain.
• If the API does not set this header correctly, CORS will block the request on your live site.

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3. Avoid Client-Side API Calls if Not Allowed

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• If the external API does not support CORS, you can’t safely call it directly from a Logic workflow that runs on the front end.
• Instead, you’ll need to proxy the request through a backend server you control that:
• Makes the API call server-side.
• Returns the data to Webflow without triggering CORS issues.

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4. Use Webflow Logic Correctly

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• Note that Webflow Logic workflows can be triggered by forms, CMS items, or schedules, but they do not have true backend/server-side execution.
• If your Logic workflow runs on the client side (e.g., triggered by a form), CORS restrictions still apply.
• Consider building the API request into a Webhook-powered Logic workflow triggered server-side (like via a form submission).

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5. Use a Serverless Function as a Proxy

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• Use platforms like Netlify Functions, Vercel, or Cloudflare Workers to build a small backend that:
• Accepts a request from your Webflow site.
• Calls the external API securely.
• Sends the response back to your site with correct CORS headers.

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6. Debugging Tip

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• Use the browser’s Developer Tools > Network tab to inspect the API call.
• Look specifically at the Response Headers to check if Access-Control-Allow-Origin is properly set.

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Summary

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CORS errors appear on deployed Webflow sites because of browser security—not Webflow bugs. To resolve them, you must ensure the API allows your domain via CORS headers or proxy the request through a server or serverless function to avoid direct frontend calls.