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 trying to update a multi-reference field in Webflow CMS via Integromat (Make). This usually results from incorrect formatting of the multi-reference field data.

1. Understand Webflow Multi-Reference Field Requirements

• Multi-reference fields expect an array of valid CMS item IDs (i.e., _id values).
• When sending data via Integromat, the field must be passed as a JSON array of strings:
  Example: ["605c9563f70c4a2be4e369e4", "605c9563f70c4a2be4e36abc"]

2. Retrieve the Correct Reference Item IDs

• Before updating, you must make a Webflow “Get all items” API request on the referenced collection.
• From the response, extract the _id values of the items you want to associate.

3. Format the Multi-Reference Field Properly in Integromat

• In the Webflow > Update Item module in Integromat:
• Use the map or array function to convert multiple referenced items into a proper JSON array of strings.
• Example using the array() function in Integromat's scripting field:
  array("605c9563f70c4a2be4e369e4", "605c9563f70c4a2be4e36abc")
• Do not send a comma-separated string or a single item unless the field is meant for a single reference.

4. Confirm Your Request Body Matches Webflow's Requirements

• Webflow expects a JSON body for updating CMS items in this format:
• "multireferencefield": [ "id1", "id2", "id3" ]
• In Integromat, make sure the multi-reference field maps to an array of strings, not a malformed object or plain text.

5. Check for Required Fields and Validation Rules

• Webflow may return a 400 error if any required field is missing or invalid, not just the multi-reference field.
• Double-check that all required fields (e.g., plain text, slug, images) are valid and included when updating.

6. Use a JSON Validation Tool if Needed

• If using a custom HTTP module in Integromat, validate the request body with a tool like JSONLint to ensure the structure is correct.

Summary

To resolve the 400 ValidationError when updating a multi-reference field via Integromat:

• Fetch and use valid Webflow CMS item _id values.
• Format them as an array of strings.
• Ensure all required fields are correctly included.
• Use Integromat's tools like array() or mapping modules to format the data correctly.

Following this structure will allow the Webflow API to accept and process your multi-reference updates successfully.