capture data from Panasonic PBX using c#

Question

Hi,

I have written the below code to capture data from Panasonic PBX(KX-TDE 100/200) and write it to a file.

But I am not able to receive any data from PBX except "-" plus whatever I send in "sendingMessage" variable.For example if sendingMessage="abcde",I will receive -abcde
Also the documentation is describing how to configure PBX box.Also for the PBX to return the data, we need to send valid credentials. How to send this valid credentials?