Payment Issue
Send this as soon as a charge is declined. It names the amount and card, puts the Update payment method button first, and explains the retry date and what pauses if the next attempt fails. Pass the amount, card ending and retry date as data, and match the consequences to your actual billing policy.
Loops
Match it to your retry schedule
Pass the amount, card ending and next retry date as required transactional data, using the dates your payment provider will actually retry. Only say that features pause or data stays safe if that is your policy. Send it as transactional email so it also reaches customers who unsubscribed from marketing, and see the Stripe payment emails guide for a short follow-up sequence.