1. Go to My Biztory do the Email setting

2. Click the "Email" column.

3. Set the Payment Overdue Email column to "Yes" for enabling the auto-send overdue emails, for the Payment Overdue Options column can select Number of days in the first box and the dropdown can select "On Due Date", "Day(s) before due date" and "Day(s) after due date".

4. Click "Save".