Cashier Paddle Checkout quantity

Hi,

does anybody know how to mark a transaction as status billed in the checkout? I want to disable the option that a user can change the quantitiy on the checkout. I am using per Seat pricing

https://developer.paddle.com/build/checkout/pass-update-checkout-items#prevent-changes-to-items-on-a-checkout -> Pass a billed transaction to Paddle.js.

Thanks!