Hello there, @jasper-simonds.
You'll be happy to know that your customer has the option to choose auto-pay recurring bills when turning on the QuickBooks payments. I'd be glad to share it with you.
Once you’ve turned on QuickBooks payments, you can now email any transactions with a Pay Now button which allows your customer to enter their credit card information.
But regarding auto-pay, this will be an internal agreement between you and your customer if they choose Pay Now or Monthly basis.
To get started, you can read through this article for the detailed steps and information: Create a Recurring Credit Card Payment.
You might also want to read this article to learn more about how to manage recurring transactions: How to Create a Recurring Invoice and Manage Recurring Transactions.
That's it! Fill me in if you have any other questions about QuickBooks payments. I'll be around if you need any help.