When Mongolians call a waiter/waitress-zuugch, you say “minii duu” (brother, sister if younger than you), “ahaa”- brother, “egchee” sister that older than you. You can pay before eating in a café or small place but in a restaurant, you usually pay after the meal.
There are days when some of the items on the menu are not available. The waiter will say baihgui- it isn’t there.
Tipping in a restaurant 5-10%. But in the countryside at local canteens rarely expected and it isn’t common.