Why am I unable to set CustomSecurityAttributes on an AAD User in C# using Microsoft.Graph.Beta?

Question

I have an attribute set named "TestSet" with the attribute "TestString". When attempting to set this attribute value as follows, an ODataError is thrown with Error.Message "Invalid property 'TestSet'.". However, I am able to set these values via the Azure UI.

if (!string.IsNullOrWhiteSpace(user.Degree))
{
    var patch = new User();
    patch.CustomSecurityAttributes ??= new CustomSecurityAttributeValue();

    patch.CustomSecurityAttributes.AdditionalData.Add("TestSet", new
    {
        OdataType = "#Microsoft.DirectoryServices.CustomSecurityAttributeValue",
        TestString = user.Degree,
    });

    await _client.Users[newUserId].PatchAsync(patch);
}

Answer 1

The issue is with how "OdataType" is serialized in JSON. Microsoft needs to update their documentation for this as what they have does not work.