You can customize the information that appears in the description of invoice and expense line items by following the below:
1) Go to "Settings" in the Left-Hand Navigation Bar, then click "Invoice Settings" or "Expense Settings" under Billing & Invoicing
2) Copy and paste the provided variable for the information you would like to show in the line item into the "Default Description for Invoice/Expense Item" box, then click "Save"
Invoice:
Expense:
If your invoice line items descriptions are not generating on your invoices, you will need to change to insure that the description is selected to appear on your invoice template.
To do this go to "Settings", click "Invoice Template" under Billing & Invoicing, click on your current invoice template, scroll down to "Customize the item table", click the check box next to "Description", then click "Save".