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