Write a late-fee reminder email for an overdue invoice. $0.01 USDC on Base per call. Calculates the late fee and returns a ready-to-send subject and body in a polite, firm or final tone. Bad input returns 400 and is not charged. Don't use this for sending email; it only returns text.
https://api.freesmallbiztools.com/v1/late-fee-notice