Call not working sometimes in sip_ua package of Dart

Question

I'm Developing VOIP application in Flutter. Got below error and call not connected not in every case but in random case its happen.

Sip Registration Snippet

static void registeredSip(SipData sp) async {
    UaSettings settings = UaSettings();

    settings.webSocketUrl = 'wss://${sp.sipDomin}:${sp.sipPort}'; 
    settings.webSocketSettings.allowBadCertificate = true;
 
    var uri = 'sip:${sp.sipUsername}@${sp.sipDomin}';
    settings.uri = uri; 
    settings.authorizationUser =  sp.sipUsername; 
    settings.password = sp.sipPassword; 
    settings.displayName = sp.sipUsername; 

    globals.helper!.start(settings);
  }

Starting Sip Call snippets below

  SIPUAHelper helperObj = globals.helper!;
  helperObj.call(typedNumber,voiceonly: true, mediaStream: null);

Error

sip_ua_helper.dart:224 ::: call failed with cause: Code: [408], Cause: Canceled, Reason: SIP ;cause=408 ;text="Request Timeout"

I'm using Sip_ua for Calling.