This API is used to fetch Ticket Details (various ticket fields like status, owner, ticket, priority etc ) including Ticket Posts.
Please check example usage of Vision Helpdesk API

Module: ticket
Operation: ticket_details

$postfields["vis_module"] = "ticket";
// This is the module under which you wish to perform operation

$postfields["vis_operation"] = "ticket_details";
// This is the operation field

$postfields["vis_ticket_id"] = 1;
// Ticket id for which you wish to get details

Below is API URL example for Get Ticket Details

JSON: 
http://visiononlinedemo.com/support/api/index.php?
&vis_txtusername=admin
&vis_txtuserpass=21232f297a57a5a743894a0e4a801fc3
&vis_module=ticket
&vis_operation=ticket_details
&vis_ticket_id=163
&vis_encode=json

XML:
http://visiononlinedemo.com/support/api/index.php?
&vis_txtusername=admin
&vis_txtuserpass=21232f297a57a5a743894a0e4a801fc3
&vis_module=ticket
&vis_operation=ticket_details
&vis_ticket_id=163

OR use "access token" to Get Ticket Details

JSON: 
http://visiononlinedemo.com/support/api/index.php? 
&vis_txttoken=T0RSbU56TmpZemxoTlRabU1XWTJOV1ZtT0RWa1ltUm1NR1F6WldJell6VT0= 
&vis_module=ticket 
&vis_operation=ticket_details 
&vis_ticket_id=163 
&vis_encode=json 

XML: 
http://visiononlinedemo.com/support/api/index.php? 
&vis_txttoken=T0RSbU56TmpZemxoTlRabU1XWTJOV1ZtT0RWa1ltUm1NR1F6WldJell6VT0= 
&vis_module=ticket 
&vis_operation=ticket_details 
&vis_ticket_id=163