Once you complete a delivery, your customer receives a notification asking them to tip. Customers aren't able to place new orders until they take action on tipping in their app.
You'll see your tips appear in your Fleet dashboard or in the "Earnings" tab of your Fleet app no sooner than 24 hours after you complete a delivery. Even if the customer tips right away, the system won't process it for at least 24 hours.
Check out some pointers on how to maximize your tips!