16-456 errors can be caused by attempting to schedule a duplicate recording on your AirTV device.
Before troubleshooting, in your Sling app, go to My DVR > Scheduled to see if the recording is already scheduled. If the recording is already scheduled, you can ignore the error.
Try the steps below to resolve the error:
Turn the AirTV device off, then turn it back on.
Open the Sling app on a mobile device or tablet and go to Settings > Over The Air Channels > Remove AirTV. After removing the AirTV, select Set Up AirTV to reconnect the device.
If you're still receiving this error after attempting the steps above, please connect with AirTV at 866-974-1354.