Walk-ins can be added when there is no WiFi or internet connection. Newly added attendees can check-in and print badges. However, the event attendance number will not update until the devices are connected to a WiFi network.
You can enable offline walk-ins from your event Dashboard:
Click on the blue Edit Event button
Scroll down to Offline Walk-in
Once enabled, some features will be unavailable.
*Note: Offline walk-ins should only be used as a last resort at a live event. Ensure that all devices are connected to a stable WiFi network.