What could be causing the recurring 400 status code in my Webflow flow test?

A 400 status code (Bad Request) during a Webflow flow test typically indicates invalid or missing data being sent to an API, webhook, or integration step.

​

1. Check API or Webhook URLs  

• Ensure the Webhook URL or Third-party API endpoint in your flow step is correctly formatted (https://...).
• Check for malformed parameters, encoding issues, or incorrect query strings.

​

2. Validate Required Fields  

• Web services return 400 when required fields are missing or empty.
• In your flow steps (like form submissions or CMS updates), verify all mandatory variables are being populated.
• Check if fields like email, ID, or token are blank or contain invalid formats.

​

3. Review Headers and Authorization  

• If using custom headers (e.g., for Bearer tokens), make sure they’re correctly configured.
• Some services require headers like Content-Type: application/json — missing or incorrect headers can trigger a 400.

​

4. Confirm Flow Trigger Data  

• If the flow is triggered by a form submission or CMS event, inspect the inbound data.
• Use the "Test trigger" function to preview sample data and ensure it includes all necessary fields.

​

5. Test the Endpoint Separately  

• Use Postman, Insomnia, or curl to send a test payload manually to the same endpoint using identical data.
• If the manual call also fails with 400, the issue is with the endpoint requirements — not Webflow.

​

6. Check CMS and Form Binding  

• For CMS collection flows, ensure the referenced collection still exists and matches the expected schema.
• For form submission flows, verify field names have not changed or been removed from the Form block.

​

Summary  

A recurring 400 error in Webflow flows is typically caused by invalid input, missing required data, or misconfigured headers. Re-check your webhook or API step, validate required fields are filled properly, and confirm your endpoint is accepting the payload structure you’re sending.