What does the tier up message say, and can I change it?

It is yours to write on Marketing → Loyalty & stamps under Customer tiers. The words {name}, {restaurant} and {tier} are filled in for you, and what the tier gives is added to the end automatically, so never type the discount or the code yourself. It goes out when a customer crosses the threshold for that tier, which is counted from delivered orders. Keep it to a sentence or two, because it lands on WhatsApp from your own number. The Loyalty & rewards tab in the docs has a guide on tiers.