HappyFox allows you to create custom fields and also mark them as 'Required-on-Ticket-Completion'. Such fields should be updated with information before closing the tickets. 

Applicable Plans: ✖️ Mighty ✔️ Fantastic ✔️ Enterprise ✔️Enterprise Plus

When a ticket is moved to a status of 'Completed' behavior, the system would check and show a pop-up box for the agents to enter the required values. Here, in this pop-up, an additional option is given for the agent to fill the fields in the ticket details page sidebar. This enables the agents to analyze the ticket details and then update the required information in the ticket details page. 

Shown below is a demo of this feature : 

Note:- This feature is not applicable while a user tries to close a ticket in ticket listing page or through bulk actions.