You'll need to first make sure that you turn on the option to display the customer and billable options for expenses. To do this, follow the steps below.
- Click Process Expenses.
- Click Preferences.
- Under the "Expenses Screen" tab, check the checkbox for "Allow to specify customer for expense?" and "Allow to specify if expense is billable?".
- Click Save.
The next time you open the "Expenses" window, you'll see the option for Customer and Billable are now visible.