If you do not receive coins after an absence, it means that you assign your staff to complete a phone order, or a car order. In this case, your staff is busy with completing these orders. They don't serve customers and as a result don't earn coins.

Please note that if you assign 2 baristas for completing orders, waiters won't bring profit as well, because there are no available baristas for preparing dishes.

Make sure there is enough furniture to serve customers. You should have bar counters for a barista and tables for waiters.

Do not forget to exit the game correctly.
On Android: when exiting, you need to press the Back button on your device, a window should pop up with the question: "Do you want to leave the current game?" Then you can check the task manager. The game should be deleted from there.
On iOS: open the App Switcher (on an iPhone with Face ID: Swipe up from the bottom edge and pause in the center of the screen. On an iPhone with a Home button: Double-click the Home button), swipe right to find the app, then swipe up on the app.

Your café will always generate the highest possible profit by following these simple rules.