Afterpay is a free service offered by retailers to shoppers - there are no upfront fees charged or any interest incurred.
The only fees that may be incurred by shoppers are late fees if your scheduled payments are unsuccessfully processed and, after being notified, you do not log in to your Afterpay account to make your payment via a different method.
Late fees for shoppers in the USA are capped at 25% of the order value.