Save multiple people/groups in a People or Group field using SP 2013 REST API

Question

I am trying to save a list item in SP 2013 using REST API.

One of the fields, named AccessRights, is a People or Groups type field.

My code works fine when I use this:

dataToSave["AccessRightsId"] = 46;
//add other fields
//post through REST API

However, I need to save multiple groups or people in this field.

Following this blog post, I am trying to send the request like this:

Instead of just group ID, I am trying to use an object that consists of the "results" property that has an array of group IDs.

This fails with the following error:

Microsoft.SharePoint.Client.InvalidClientQueryException",

"message":{"lang":"en-US","value":"An unexpected 'StartObject' node was found when reading from the JSON reader. A 'PrimitiveValue' node was expected.

I've tried to use both string and number values in the array ("47" and 47), neither work.

What's the correct way to save multiple people or groups via REST API into a People or Group field?

Answer 1

The error says that PrimitiveValue expected.

That means SharePoint assumes your actual field type is single-value, you need to switch it to multiple selection.

Answer 2

Turns out this was because the "Allow multiple selections" option in the column settings was off. Need to change it to "Yes":