Missions operate in Reminder phase when the current timestamp is before the invoice's due date. During this phase: Multiple reminder emails are sent at configured intervals (e.g., 14 days before, 7 days before, 1 day before) Progress displays as "X/Y reminders" where X = reminders sent, Y = total reminders configured Next Send calculated based on the next unsent reminder rule (largest days-before value not yet executed) Transitions to Overdue phase automatically once due date passes Configuration controlled by Portal > Settings > Payment Reminder tab Missions automatically switch to Overdue phase when the current timestamp is after the invoice's due date. During this phase: Recurring overdue emails sent at fixed intervals (e.g., every 3 days) until stopped Progress displays as "Z overdue