Cannot change expense billable/unbillable setting

Question
Cannot change expense billable/unbillable setting?

When entering expenses, there is a checkbox indicating if an expense is billable or not. This checkbox is checked for some expenses and unchecked for others. The user would need to change this sometimes, but the checkbox is disabled and cannot be changed.

Where does this value come from and how can we enable the user to change it himself?

Answer
Whether an expense is billable or unbillable by default is determined by the project billable setting. To enable users to override this setting during expense entry, in the project 'expense access' tab, there is a settings that allows users to override the billable status.

Note
Overriding is only possible for billable projects, so that users can create both billable and unbillable expenses. It is not possible to create a billable expense for an unbillable project.