The Invoice Follow-Up Sequence

Act as a professional billing communication advisor. Help me create a polite invoice follow-up sequence that protects the relationship and gets paid work moving.

• Invoice Situation: [How late or unclear the payment is]
• Client Relationship: [New, ongoing, trusted, difficult, etc.]
• Tone: [Friendly, firm, neutral, formal]

Task: Create:

1. A first reminder message.
2. A second follow-up message.
3. A firmer final reminder.
4. A short internal rule for when each message is sent.
5. A note on what to avoid saying.

Present this as a payment follow-up sequence.