Issue Updating Multi-Value Lookup Field in SharePoint List Item Using Microsoft Graph API

Hello Everyone!

I'm encountering an issue when trying to update a multi-value lookup field in a SharePoint list item using the @microsoft/microsoft-graph-client library. My code successfully updates fields of type string and number, but I’m facing problems with a field of type array (multi-value lookup).

The field in question is called users, which references multiple IDs from another SharePoint list. Below is the field’s metadata:

{
  "columnGroup": "Custom Columns",
  "description": "",
  "displayName": "users",
  "enforceUniqueValues": false,
  "hidden": false,
  "id": "xxxxxx",
  "indexed": false,
  "name": "users",
  "readOnly": false,
  "required": false,
  "lookup": {
    "allowMultipleValues": true,
    "allowUnlimitedLength": false,
    "columnName": "ID",
    "listId": "xxxxxxx"
  }
}

Here’s the relevant code I’m using to update the list item:

const res = await client
  .api(`/sites/${siteID}/lists/${listId}/items/${itemId}`)
  .expand("fields")
  .patch({
    fields: updateData,
  });

The update works fine when I set a single value for the users field. However, when I attempt to update it with multiple IDs (e.g., [9, 12]), the request completes without errors, but the field does not update in SharePoint.

I’ve tried several formats for the updateData payload. My most recent attempt sugested by copilot was:

updateData = {
  "users": {
    "@odata.type": "Collection(SP.FieldLookupValue)",
    "results": [
      {
        "LookupId": 9
      },
      {
        "LookupId": 12
      }
    ]
  }
};

Despite this, the field still doesn’t update. I’ve also experimented with other formats, such as passing an array of IDs directly, but none have worked for the multi-value case.

Could you please provide guidance on the correct payload format for updating a multi-value lookup field using the Microsoft Graph API? Any examples or documentation references would be greatly appreciated.