Hangup cause and hangup source information for every call is available in the Call Detail Record (CDR) of the call.
Hangup information is also included in callback requests sent on call hangup.
For outbound API calls, the hangup information is included in the payload sent to the hangup_url specified in the Make Call API request.
For incoming calls, this information is included in the payload sent to the hangup_url specified for the associated Plivo Application.
For calls initiated using <Dial> XML, this information is included in the payload of DialHangup events sent to the Dial callbackUrl.
For the comprehensive list of possible hangup causes and hangup sources, check out our documentation here.