If a payment has already been made, you can write an internal note about it on the details page of that payment in your MoonClerk dashboard. If you export the data for the payment, this note will also appear on the spreadsheet.
1) Click on the Payments button in your account's main navigation
2) Click on the payment that you'd like to add a note to
3) Scroll down to find the Internal Note section and click Add Note
4) Type in your internal note
5) Click Create Note
6) You can come back to the Internal Note section at any time to edit or delete this note.