What could be causing the error in the console when trying to integrate Mailchimp with Webflow and the form is not submitting?

When integrating Mailchimp with a Webflow form, console errors during form submission usually point to a setup or configuration problem. Here's how to diagnose and fix it:

1. Check Form Action URL

• Inspect the form’s Action URL in the Webflow Designer.
• Go to the Form Settings and check if the form’s Action is set to the correct Mailchimp POST URL (it should look something like https://[dc].list-manage.com/subscribe/post?u=[uid]&id=[listid]).
• Common issue: A missing or incorrect endpoint URL will cause form submissions to fail silently or with a 404/405 error.

2. Inspect CORS and Same-Origin Policy

• Mailchimp forms don’t typically support direct AJAX POST requests from foreign domains due to CORS restrictions.
• If you see an error like “Access-Control-Allow-Origin” missing in the console, it means your front-end cannot communicate directly with Mailchimp.
• Solution: Instead of AJAX, Webflow’s native form should perform a traditional POST (page reload with submission) or use a third-party integration tool like Zapier.

3. Verify Hidden Input Field Values

• Ensure that hidden fields like u and id are inside your form and correctly populated.
• Missing or wrong values for these fields will cause Mailchimp to reject the request.
• Double-check the action URL parameters match with the Hidden Fields inside your form.

4. Check Form Method and Encoding

• Verify that your form method is set to POST and the encoding type is set to application/x-www-form-urlencoded (default for Webflow forms).
• Incorrect settings might cause incorrect submissions or no submission at all.

5. Identify Errors From Spam Protection (reCAPTCHA)

• If you enabled reCAPTCHA within Webflow but didn’t configure it properly, Mailchimp won't accept the submission.
• Check for console errors related to captcha verification or token missing.
• Either properly configure reCAPTCHA or disable it for this form.

6. Review Custom Code Conflicts

• If you added custom JavaScript to handle the form submission through fetch/XHR, it might conflict with Webflow’s built-in handlers.
• Check for JavaScript errors in the console like Uncaught TypeError or ReferenceError at form submission.

Summary

Usually, a Mailchimp and Webflow form submission error is due to wrong action URL, CORS issues, missing hidden fields, or conflicting custom code. Double-check all form settings and ensure you’re not relying on AJAX for interaction with Mailchimp without using a backend proxy or integration service.