If a particular expense should not be invoiced for the time being, you can mark it as non‑billable. The Change status > Non‑billable function is available both on the expense list and in the ribbon of an individual expense. 

This sets the expense to non‑billable status, causing the Total field of the entry to change to zero and become inactive. After this, you can create an invoice from the matter without the expense being included on the invoice. 

You can return an expense in Non‑billable status back to active by selecting Change status > Billable. The Total amount will then return to its original value and become active again, and the expense can be included in the next preliminary invoice or invoice created from the matter.