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 when updating a multi-reference field in Webflow via Integromat (now Make). This typically means the payload being sent is not formatted correctly, especially for multi-reference fields which require specific structure.

1. Understand Webflow’s Multi-Reference Field Format

• Multi-reference fields must be sent as an array of CMS item IDs (strings).
• You cannot send a single string or an improperly formatted JSON object.
• The value must look like: ["itemID1", "itemID2"]

2. Retrieve Correct CMS Item IDs

• Make sure you’ve retrieved valid Webflow CMS item IDs (not slugs or names) from the referenced collection.
• Use the Webflow > Get Item or Webflow > List Items modules in Make to collect these IDs.

3. Format the Array Properly in Make

• When using the Webflow > Update Item module, manually structure the multi-reference field like this:
• Inside the “Body parameters” mapping section, for your multi-reference field key, insert an array of item IDs.
• Example: If the field API name is related_articles, input:
• ["{{id1}}","{{id2}}"] (Replace {{id1}} and {{id2}} with Make variables or map them dynamically from a previous module)

4. Ensure Field API Name Matches Exactly

• Go to Webflow CMS Schema to confirm the API name of the field.
• Make uses API names — double-check for typos, underscores vs. dashes, or extra characters.

5. Check for Null or Empty Arrays

• Sending null or an empty array ([]) can also cause validation errors if the field is required or expects an array with values.
• Ensure you're only updating this field if you have at least one referenced item ID.

6. Use Custom HTTP Module for More Control (Optional)

• If the standard Webflow module fails, use Make's HTTP module for a PATCH request to:
• https://api.webflow.com/collections/{collectionid}/items/{itemid}
• Set headers correctly:
• Authorization: Bearer your_token
• accept-version: 1.0.0
• Content-Type: application/json
• Structure your body like { "fields": { "multireferencefield": ["itemid1", "itemid2"] } }

Summary

To fix the 400 ValidationError in Make when updating a Webflow multi-reference field, ensure you're passing an array of valid CMS item IDs, using the correct API field name, and formatting the request properly. Use Webflow’s own modules or a custom HTTP request to troubleshoot further.