How can I resolve the "The operation failed with an error. [400] ValidationError: Invalid request body" issue when trying to update a multi-reference item field in a CMS collection using Integromat with Webflow?

You're encountering a 400 ValidationError because the Webflow API expects a specific format for multi-reference fields when updating CMS items via Integromat (now Make). Here's how to resolve it.

1. Understand the Required Format

• Multi-reference fields require an array of item IDs (e.g., ["605c5b1b7bd8bdf168fa674c", "605c5b1b7bd8bdf168fa674d"]).
• Each ID in the array must be a valid CMS item ID from the collection you're referencing.
• The request must use the PATCH method and set fields.{multiRefFieldName} to the array of IDs.

2. Collect the Correct Item IDs

• In your Integromat scenario, ensure you're retrieving the referenced item IDs through a Webflow list module or storing them from previous steps.
• Do not send plain text (e.g., names or slugs) — Webflow only accepts CMS item IDs.

3. Format the Body Correctly in Integromat

• When using the Webflow API Make a request module, ensure your JSON body follows this structure:
• Example: { "fields": { "authors": ["605c...abc", "605d...def"] } }
• Replace "authors" with your actual multi-reference field name (case-sensitive and no brackets or quotes).
• Ensure the value is an array of correct CMS item IDs, not a string or comma-separated string.

4. Check for Extra or Missing Fields

• Webflow is strict about fields — do not include extra fields that are not being updated.
• If you're updating only the multi-reference field, leave others blank or omit them entirely unless they're required (like slug, depending on your setup).

5. Verify Field Name and Permissions

• Double-check the field name in your collection settings on Webflow.
• Make sure your Webflow API token has full CMS permissions.
• Confirm the item you're updating exists and is published in the same site/version.

6. Use JSON Module for Better Control (Optional)

• Instead of the default Webflow module, consider using HTTP > Make a request in Integromat.
• Set Method to PATCH.
• Set the URL to https://api.webflow.com/collections/{collection_id}/items/{item_id}?live=true.
• In Headers, add:
• Authorization: Bearer YOUR_API_TOKEN
• Content-Type: application/json
• accept-version: 1.0.0
• In the request body, manually craft the JSON ({"fields": {...}}) as described above.

Summary

To fix the 400 ValidationError for a multi-reference field in Webflow, ensure you're passing a properly formatted array of valid CMS item IDs to the correct multi-reference field, using the PATCH method and correct JSON structure. Validate that all field names are accurate and that the request body contains no invalid or misformatted data.