How to implement user status monitoring?

Question

C++ / C#

I am writing a program, one of the functions of which is: calls through the 3cxphone program. The essence of the problem is that in the 3cx phone contact list, the customer wants to see the user's status icon (Online / Offline / Away) How can I implement this function. The program is written in C#. Microsoft Visual Studio Community Development Environment.
Photo example.

Answer 1

https://habr.com/company/3cx/blog/265653/ It seems that the topics you need are revealed there