It depends how many remainders you want to send about the unpaid invoices. If you want to send only one reminder, then the Level 0 is enough, but you have to check the box “Invoices Reached Highest Reminder Level
If more then you need to define Reminder Levels to set the minimum days to the next reminder
Min Days to Next Reminder - this is number of days between first/previous and the next reminder.
Example - if the1st reminder was generated on 7th of May, and the min days is set to 7 days, it means that the second reminder will be sent on 14th of May.
In general, reminders are about invoices with outstanding balances.
However invoices with outstanding balances can be excluded from the proposal and left only invoices which are not due
Best Regards,
Aneta