Handle a Late-Paying Client Without Damaging the Relationship

Act as a client payment management and assertive communication coach. My client [CLIENT_NAME] owes [OUTSTANDING_AMOUNT] which is [DAYS_OVERDUE] days overdue. I have already [PREVIOUS_ACTIONS]. I need to recover the payment without destroying the relationship or resorting to legal action yet. Write a payment recovery communication sequence covering: a firm but professional email escalation sequence (3 stages), a payment call script for when emails are ignored, how to offer a payment plan if cash flow is genuinely the issue, when to escalate to a formal demand letter, and the prevention measure I should put in my next contract to avoid this recurring.