Dunn

• invoice_due_date — Exact due date for an invoice from its date and payment terms ("net 30", "due on receipt", "EOM", "net 30 EOM", "2/10 net 30"), including any early-payment disc
• late_fee_calculator — Works out a late fee: the amount, the new total, the exact day it applies, a ready-to-use line for the invoice, and whether the fee is in the usual range.
• how_late_is_this_invoice — How many days late an invoice is (or until it is due), and what to send the client now and next, following a proven reminder schedule.
• payment_reminder_email — Writes the right payment reminder for where the invoice is now (before due, due today, late, or a final notice), with subject line. Polite by default; firm on r

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