This article explains how to add unbilled expenses to your invoices in FreeAgent
To add an expense to an invoice you will first need to associate that Expense with a Project. To do this simply select 'Link to Project' when adding the Expense and choose the project you want to link it to.
To then add your unbilled expenses to an invoice when you first add, or subsequently edit, the invoice, you'll find fields on the form labelled 'Include Unbilled Items', 'Expenses' and 'Estimates'.
From the 'Include Expenses' dropdown, you can choose to either include each expense on a separate line or to include them all on one line.
Including them on separate lines will add each expense as a separate invoice item. Including them all on one line will group together all expenses as one line item and all mileage claims (with the same mileage rate) as another line item.