Automated client reminders: message library and timing rules

Create an automated client reminder system for {use_case}.

Inputs:
- Trigger events (missing docs, unpaid invoice): {triggers}
- Client segments (new vs recurring): {segments}
- Communication channels: {channels}
- Tone guidelines: {tone}
- Escalation rules: {escalation_rules}

Output:
1) Message templates by trigger and stage (1st reminder, 2nd, escalation).
2) Timing rules and stop conditions (when to stop nudging).
3) Personalization fields to merge (client name, due date, items).
4) Compliance notes (opt-out, confidentiality).

Keep templates professional and short.