Can't Receive incoming call when connected to plivo using ws but can receive when connected over tcp

[shreyanshcladbe]

void start(String username, String password) {
UaSettings settings = UaSettings();

settings.webSocketSettings.allowBadCertificate = true;
settings.webSocketSettings.userAgent = 'Dart/2.8 (dart:io) for OpenSIPS.';
settings.tcpSocketSettings.allowBadCertificate = true;
settings.transportType = TransportType.WS;
settings.webSocketUrl = 'wss://client.plivo.com/signalling';
settings.uri = 'sip:$username@phone.plivo.com';
settings.host = 'phone.plivo.com';
settings.port = '5060';
settings.authorizationUser = username;
settings.password = password;
settings.displayName = username;
_helper.addSipUaHelperListener(this);
_helper.start(settings);

}

above are the settings that i did

1. when it is set to transporttype.tcp then it gets INVITES that plivo sends for incoming call
2. when it is set to transporttyoe.ws then it does not get those INVITES that plivo sends for incoming calls