Sometimes your iPads may need to be restarted a few times if you can't connect to WiFi.
1. Verify that other devices in the restaurant are connecting with the internet.
2. After verifying, press the "HOME" button -> "SETTINGS" - > Tap on WiFi- > Turn WiFi off for 10 seconds - > Turn WiFi back on. Verify that the iPad is connected to the WiFi network and that the connection is stable.
3. If you still can't connect to the internet, perform a hard reset: press and hold the "HOME" and "STANDBY" buttons (at top of the iPad). Keep them held for approximately 10-12 seconds until device restarts and you see the Apple logo.
4. If it's still not working, contact your internet provider or reboot your router.