由于错误403(禁止)，Google . net API失败

下面的代码片段应该返回信标列表。当有谷歌API控制台生成API密钥时，我已将我的公共IP地址列入白名单，并与API密钥相关联。当代码调用ExecuteAsync()方法时，我一直收到错误码403(禁止)的异常。我可能做错了什么?如何减轻这个问题?

public async void TestApiKey()
{
    var apikey = "739479874ABCDEFGH123456"; //it's not the real key I'm using
    var beaconServices = new ProximitybeaconService(new Google.Apis.Services.BaseClientService.Initializer
    {
        ApplicationName = "My Project",
        ApiKey = apikey
    });
    var result = await beaconServices.Beacons.List().ExecuteAsync();
    // Display the results.
    if (result.Beacons != null)
    {
        foreach (var api in result.Beacons)
        {
            Console.WriteLine(api.BeaconName + " - " + api.Status);
        }
    }
}