A TAPI-driver for your phone system is required to operate this software.
A TAPI-driver is a system component that is provided by the manufacturer of your telephony device (either free of charge or for a fee).
The TAPI-driver connects the CTI software to the telephony terminal device. Each TAPI-driver supports different functions depending on the implementation. Not all functions which you can perform on the phone itself are always available on the PC.
TAPI-drivers are installed in Settings - Control Panel - Phone and Modem Options - Options - Advanced.