You need to enable Queue at the organization level and then configure at the center level for the Queue to function.
To enable queue at the organizational level
1. Navigate to Admin > Organization > Organizations > Settings > Queue/Guest Kiosk.
The Queue/Guest Kiosk settings opens.
2. Locate and select the Enable Admin Queue checkbox.
3. Click Save.
Queue is enabled at the organization level and now you can configure Queue and its settings in center level.