Go to Settings → Chasing customers automatically.
1.Tick what you want chased: overdue invoices, unanswered estimates, or both.
2.Set the days. For invoices these count from the due date; for estimates, from when you sent it.
3.Save.
It is off until you turn it on.
When it stops
On its own, the moment the document changes — paid, voided, accepted, declined, or past its date.
Three at most
A fourth reminder does not collect anything. It teaches the customer to filter the address your real invoices arrive from, and then the one that matters never gets read.
One customer you do not want chased
Open that document and silence it. A switch that only works for everyone is a switch nobody dares use when somebody is mid-dispute.