Each monitor in your system has an address, which you can view and edit in its settings. Check the master monitor’s Monitor Address under Settings > Installer > Current Address and make sure it is set to 00 or 00.00, then re-try the call. 

You should also check that your monitor is not set to Do Not Disturb.

If this does not resolve the problem, or if the door station does not respond at all when a call is made, there may be an issue with the power supply.

In this case, please contact your installer and ask them to check your system.