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?

You're encountering a CORS policy error when using Webflow Logic to call an external API. It works in Designer preview but fails on the deployed site, indicating a client-side browser restriction caused by cross-origin requests.

1. Understand the Environment Differences

• Webflow Designer preview uses a proxy or development environment that may not enforce browser-level CORS in the same way as published sites.
• Upon publishing, Webflow Logic runs in the browser unless explicitly configured to run server-side — meaning real CORS rules will apply based on the target API's headers.

2. Determine the Type of Webflow Logic Execution

• Client-side Logic (e.g., triggered by form submissions or button interactions): These result in browser-based fetch requests which are subject to CORS.
• Server-side Logic workflows (e.g., triggered by CMS entry creation, form submissions with Logic-only processing): These run on Webflow's backend and are not subject to CORS policies.

3. Check the API's CORS Headers

• The external API must respond with the appropriate Access-Control-Allow-Origin header.
• To allow calls from your specific site, the API must return:
• Access-Control-Allow-Origin: https://yoursite.webflow.io or your custom domain.
• Alternatively: Access-Control-Allow-Origin: * (not recommended for private APIs).

4. Use a Webhook Instead of a Direct Fetch

• If the external API supports it, use a webhook to push data to Webflow rather than pulling it from Logic.
• This avoids browser-based execution entirely, sidestepping CORS.

5. Use Server-Side Logic Triggers Whenever Possible

• To avoid CORS issues entirely, trigger your Logic workflow using:
• Form submissions that are processed solely with Logic (without client-side API calls).
• CMS or Ecommerce events, which initiate Logic server-side.

6. Use a Secure Proxy Server

• If you control a server or serverless environment (e.g., Vercel, Netlify), set up a proxy that:
• Fetches from the external API.
• Adds the appropriate CORS headers.
• Webflow frontend Logic then calls your proxy instead.
• Webflow itself does not offer built-in proxying features.

Summary

You're hitting a CORS error because your deployed Webflow site executes Logic in the browser, and the API you're calling doesn't allow requests from your domain. To fix this, use server-side Logic workflows, update the API’s CORS headers, or implement a secure proxy to handle the request.