C#　unity API　エラーについて

Unityで以下のプログラムでAPIから緯度経度を取得しようとしたのですが、新規プロジェクトを作成し、オブジェクトにこのアセットをアタッチしたのですが下記のエラー文が出てしまいました。

C#
1using System.Collections;
2using System.Collections.Generic;
3using UnityEngine;
4using Newtonsoft.Json;
5using System.Net;
6using System.Linq;
7
8public class api : MonoBehaviour {
9
10	// Use this for initialization
11	void Start () {
12        var parm = new Dictionary<string, object>();
13        parm["type"] = 1;
14        parm["count"] = "5000";
15        parm["format"] = "json";
16        var urlParam = string.Join("&", parm.Select(item => string.Format("{0}={1}", item.Key, item.Value)).ToArray());
17        var url = string.Format("https://maps.googleapis.com/maps/api/place/nearbysearch/json", urlParam);
18
19        var client = new WebClient();
20        client.Encoding = System.Text.UTF8Encoding.UTF8;
21        var text = client.DownloadString(url);
22
23        var result = JsonConvert.DeserializeObject<List<googleW>>(text);
24
25        Debug.Log(result);
26
27    }
28	
29	// Update is called once per frame
30	void Update () {
31		
32	}
33}
34

エラー文

TlsException: Invalid certificate received from server. Error code: 0xffffffff800b010a
Mono.Security.Protocol.Tls.Handshake.Client.TlsServerCertificate.validateCertificates (Mono.Security.X509.X509CertificateCollection certificates)
Mono.Security.Protocol.Tls.Handshake.Client.TlsServerCertificate.ProcessAsTls1 ()
Mono.Security.Protocol.Tls.Handshake.HandshakeMessage.Process ()
(wrapper remoting-invoke-with-check) Mono.Security.Protocol.Tls.Handshake.HandshakeMessage:Process ()
Mono.Security.Protocol.Tls.ClientRecordProtocol.ProcessHandshakeMessage (Mono.Security.Protocol.Tls.TlsStream handMsg)
Mono.Security.Protocol.Tls.RecordProtocol.InternalReceiveRecordCallback (IAsyncResult asyncResult)
Rethrow as IOException: The authentication or decryption has failed.
Mono.Security.Protocol.Tls.SslStreamBase.AsyncHandshakeCallback (IAsyncResult asyncResult)
Rethrow as WebException: Error getting response stream (Write: The authentication or decryption has failed.): SendFailure
System.Net.HttpWebRequest.EndGetResponse (IAsyncResult asyncResult)
System.Net.HttpWebRequest.GetResponse ()
System.Net.WebClient.GetWebResponse (System.Net.WebRequest request)
System.Net.WebClient.DownloadDataCore (System.Uri address, System.Object userToken)

このエラー文を調べたのですが、証明書？がうまくGetできていないみたいな事が書かれていたのですが、いまいち私自身が分かっていませんので、分かる方いましたらお手数ですがご教授していただければ幸いです。