Webrtc: Unable to retrieve TURN server

Question

I am trying to use webrtc.framework along with libAppRTCMobile_lib.a for making a native app same as AppRTCMobile for ios. While calling connectToRoomWithId we are getting the below message. Please help me why TURN server is giving the below error message.

"(ARDAppClient.m:234 -[ARDAppClient connectToRoomWithId:settings:isLoopback:]_block_invoke): Error retrieving TURN servers: The request timed out."

Code Snippet:

ARDSettingsModel *settingsModel = [[ARDSettingsModel alloc] init];
self.client = [[ARDAppClient alloc] initWithDelegate:self];
[self.client connectToRoomWithId:self.roomName
                        settings:settingsModel
                      isLoopback:NO];

Thanks in advance