AgoraRTM client login failure RtmUnauthenticatedError: Error Code 5. Signature verification failed. about rtm HOT 6 CLOSED

                var appCertificate = Agora_API_SECRET;//App certificate
		var uid = _Uid;
		uint _expiredTs = 0;
		AccessToken token = new AccessToken(apiKey, appCertificate, channelName, uid);
		token.addPrivilege(Privileges.kJoinChannel, _expiredTs);
		token.addPrivilege(Privileges.kPublishAudioStream, _expiredTs);
		token.addPrivilege(Privileges.kPublishVideoStream, _expiredTs);
		string strToken = token.build();
		return strToken;