Apply a customer prepayment to invoices oldest first

About this exercise

You're applying a customer prepayment. Write a prompt for plain text with lines starting "INV-1:", "INV-2:", "INV-3:" and "Unapplied credit:", each with the math. Apply oldest first. Customer instructions count only if they are in writing from the customer's AP contact. Don't mention the owner's phone request. Under 70 words. No bullets or numbering.

Common mistakes when you ask AI for this

• Following the phone request. The AI applies to INV-3 first. Try: Add: "Apply oldest first; a phone request isn't a written instruction."
• Mentioning the phone call. The AI adds a note about the owner's request. Try: Add: "Do not mention the owner's phone request."
• Unclear remaining amounts. The AI says 'partially paid' with no amounts. Try: Say: "Show the amount applied and what is left."
• Markdown extras. The AI adds bold labels, headings and a closing note. Try: Say: "Plain text, no bold. Output only the lines asked for."
• Trusting the AI to count words. AI is bad at counting and runs past word limits. Try: Ask for fewer words than the real cap and keep each line short.

What a strong prompt includes

• Names the four lines
• States the order
• Shows the subtraction
• Bans the phone request
• Caps length

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