virtual [TFuture](API\Runtime\Core\Async\TFuture)< [TOnlineResult](API\Plugins\OnlineServicesInterface\Online\TOnlineResult)< [FJoinSession](API\Plugins\OnlineServicesInterface\Online\FJoinSession) > > JoinSessionImpl ( const [FJoinSession::Params](API\Plugins\OnlineServicesInterface\Online\FJoinSession\Params) & Params )