How are Callbackhunter and UpToСall services arranged?

Question

Telephony

How are Callbackhunter and UpToСall services arranged? As far as I understand, everything is fully automated here. After pressing the button on the site, a call comes to the manager (where exactly?). The manager calls the client back. Or does he not call back with his hands, but again, the interaction goes through the service after the manager picked up the phone?
Where can I read the technical details? And then it became very interesting.

Answer 1

from a button on the site, a request with the client number (this is the one who pressed the button) in the web-API,
it pulls the manager number from the database and queues for processing , it
is removed from the queue by the handler, issuing IP-PBX tasks API interaction with PBX
further from anyone as possible three primitive scenarios:
A call to the manager can be made both via the classical telephone network and via SIP to his own PBX.