Need To Move Window Unit:

In order fo it to work correctly, the Window Unit must be placed in an area where there is 3G coverage.

To help with placement you can:

Use your handset's signal meter to measure the 3G signal strength (number of bars displayed) around your home. A 3G icon must be displayed next to the bars (the icon may actually say 3G, 4G, or H). Place the Window Unit where you have the most 3G signal.

Make sure that the Window Unit has not been placed very close to a 3G router or other Wi-Fi device.

Did moving the window unit resolve the issue?