How do I make cost centres and references mandatory?

How do I make cost centres and references mandatory?

To make these settings mandatory for employee travel, simply go to the ‘accounts’ section of the admin panel and then to ‘settings’. 

Here, you can tick the boxes beside ‘employees are required to enter a reference’ and ‘employees are required to enter a cost centre’ to enable this setting. Once this has been done, employees will be unable to book on the company account without entering them, thus preventing unauthorised journeys.