This API is used to Get Service Catelogs
Please check example usage of Vision Helpdesk API

Operation : view_services
Module : setting

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

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

Below is example API URL to get list of service catelogs

XML:
http://visiononlinedemo.com/support/api/index.php?
vis_txtusername=admin
&vis_txtuserpass=21232f297a57a5a743894a0e4a801fc3
&vis_module=setting
&vis_operation=view_services
JSON:
http://visiononlinedemo.com/support/api/index.php?
vis_txtusername=admin
&vis_txtuserpass=21232f297a57a5a743894a0e4a801fc3
&vis_module=setting
&vis_operation=view_services
&vis_encode=json

OR use "access token" to get list of service catelogs

XML:
http://visiononlinedemo.com/support/api/index.php?
vis_txttoken=WXprMk1UY3dZV1V6WWpZeU16RmpOelF3TVdReE5UWTJOVGMyTm1VeU4yUT0=
&vis_module=setting
&vis_operation=view_services

JSON:
http://visiononlinedemo.com/support/api/index.php?
vis_txttoken=WXprMk1UY3dZV1V6WWpZeU16RmpOelF3TVdReE5UWTJOVGMyTm1VeU4yUT0=
&vis_module=setting
&vis_operation=view_services
&vis_encode=json