Related Questions:
Where do I add Invoice notes?
Can I add a note to an Invoice that is only meant for that invoice?
How do I add stuff to the notes section on an invoice?
Answer:
You can add notes to your Invoices one of two ways:
During Invoice creation:
Add an Invoice
Add a Note to the Notes section
Enter in the rest of the required/appropriate information
Click Save
To an existing Invoice:
Edit the existing Invoice you want to add a note to
Scroll down to the Notes section below the Invoice items/summary
Click the Edit button (pencil icon)
Enter your Note into the Notes section of the Edit Invoice window
Click Save