Payment Invoice
Send this a few days before a recurring charge so customers know it is coming. It shows the amount due, the plan and the charge date, with a button to view the full invoice and a line on how to change the card first. Pass the invoice number, amount and date as data, and link the button to the hosted invoice.
Loops
Send the numbers as data
Pass the invoice number, amount, plan and charge date as required transactional data, formatted the way they appear on the invoice, and test a missing value before publishing. Link the button to the hosted invoice and the billing line to the page where customers change their card. If you bill through Stripe, the Stripe payment emails guide shows how to turn Stripe events into emails.