virtual [TOnlineAsyncOpHandle](API\Plugins\OnlineServicesInterface\Online\TOnlineAsyncOpHandle)< [FAddSessionMember](API\Plugins\OnlineServicesInterface\Online\FAddSessionMember) > AddSessionMember ( [FAddSessionMember::Params](API\Plugins\OnlineServicesInterface\Online\FAddSessionMember\Params) && Params )