WebClient throwing TlsException Unity 2017.4.15f1

This piece of code is throwing a TlsException in Unity 2017.4.15f1, I've looked at other questions but no solution appears to work anymore. I vaguely understand this is an issue around certificates(?)

Code (CSharp):

1.         private void Start()
2.     {
3.         var client = new WebClient();
4.         var text = client.DownloadString("https://jsonplaceholder.typicode.com/posts/1");
5.         Debug.Log(text);
6.     }

// --- ERROR THROWN

TlsException: The authentication or decryption has failed.
Mono.Security.Protocol.Tls.RecordProtocol.ProcessAlert (AlertLevel
alertLevel, AlertDescription alertDesc)
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)