为服务主体设置ReadOverrideEffectiveIdentity时收到Forbidden响应

我正在为Power BI中的SSAS实时连接报表创建嵌入令牌，排查问题时明确需要为服务主体配置ReadOverrideEffectiveIdentity权限。我已经按步骤验证过该服务主体具备所需权限，但执行以下C#代码和API请求时，均返回Forbidden响应：

using System;
using System.Collections.Generic;
using System.Net.Http;
using System.Threading.Tasks;

namespace ConsoleApp1
{
    class Program
    {
        static async Task Main(string[] args)
        {
            using var client = new HttpClient();
            var values = new Dictionary<string, string>
            {
                { "identifier", "APPLICATION ID" },
                { "datasourceAccessRight", "ReadOverrideEffectiveIdentity" }
            };
            var content = new FormUrlEncodedContent(values);
            var response = await client.PostAsync("https://api.powerbi.com/v1.0/myorg/gateways/GATEWAYID/datasources/DATASET/users", content);
            var responseString = await response.Content.ReadAsStringAsync();
            Console.WriteLine(responseString);
        }
    }
}

我还尝试了以下API请求，同样收到Forbidden响应：

POST  https://api.powerbi.com/v1.0/myorg/gateways/GATEWAYID/datasources/DATASETID/users

Request Body JSON 
{ 
    "identifier": "APPLICATION ID", 
    "datasourceAccessRight": "ReadOverrideEffectiveIdentity" 
}

内容的提问来源于stack exchange，提问作者NutellaKing