How does a customer check how many stamps they have?

On the card on their phone, which shows the live count and updates itself when a stamp lands. They do not have to open anything or ask your staff. When a reward is ready the card shows that too, with the code and its expiry if you use codes, and a WhatsApp message says the same. Customer loyalty at a restaurant only works when people can see their progress, and the card in their pocket is where they see it. The Loyalty & rewards tab in the docs explains what the card shows.