This article covers how to:
Add custom fields
Click Settings → CRM → Fields → Ticket → Add field:
Choose a field type to add and click next:
Restrict to specific ticket types
For each field, you can restrict it to specific ticket types. This means that depending on the selected ticket type, certain custom fields will be displayed inside a ticket.
Select the ticket types under Restrict to type. The list shows the ticket types set up in Settings → Customer support → Ticket settings. If you leave Restrict to type empty, the field is shown on all tickets.