Summary
As a good practice, add a customer's check number in the New Payment window in either the Reference # box or the Receipt # box.
Key Point
Use the Deposit Report to find checks when you don't know the customer
To search for a check number:
From the Dashboard, click Reports
Click Deposit
Filter the From - To Date to apply a date range
Click Add Filter
Click Payment Method
Click Check
The check number will appear in either the REF FLD column or the RCPT # column.