The waiters (many, low-trust) were transferring orders to cashiers (few, high trust) by showing them QR code that transferred data to the cashiers' apps.

Then the waiter paid the cashier (in advance), got the bill to give to customer and order tickers (printed on a bluetooth POS printer with a cutter, so they were already separated) to recieve the goods (grouped by stations that gave out the goods, food, drinks ...). The stations took the order tickets and gave them goods. The waiters delivered them to customers and used the bill to get cash from the customer.

The waiters could use their own starting money and just stop selling at any point, or got it from the main cashier and had to return the same amount at the end.

It sounds like the Credit Card Processing system at the cashier had internet for processing credit cards etc. but the waiter app has no internet dependencies since it can transfer the order to the cashier system.