The Freshservice developer documentation has supporting_email as one of the properties sent to the app onConversationCreate. This is essentially the email from which the reply is sent to the developer.
However, both in the sample payloads that appear in local simulation (fdk run on /web/events/) or in the documentation sample JSON this attribute is missing. I guessed this might be something that isn’t captured in the sample payloads alone.
But when I tried to get the logged conversation payload in the production
{
"iparams":{..},
"region":"US",
"data":{
"conversation":{
"body":"<div>I have more questions to ask, so I'm asking.</div>\n",
"is_body_truncated":false,
"body_text":"I have more questions to ask, so I'm asking.",
"is_body_text_truncated":false,
"id":14022037361,
"from_email":null,
"bcc_emails":[
],
"user_id":14001358196,
"ticket_id":23,
"ticket_group_id":null,
"ticket_requester_id":14001358196,
"ticket_responder_id":null,
"ticket_department_id":null,
"ticket_display_id":"SR-23",
"private":false,
"incoming":true,
"source":2,
"cc_emails":[
],
"to_emails":[
],
"created_at":"2022-01-10T03:57:45-05:00",
"updated_at":"2022-01-10T03:57:45-05:00",
"attachments":[
]
},
"actor":{
"profile_id":14001XX8196
}
},
"account_id":"251XX03",
"domain":"subdomain.freshservice.com",
"event":"onConversationCreate",
"timestamp":1641805065.3502939
}
The supporting_email is missing 
