According to Apple, when you sign up for a 3-day trial, you may get charged within the last 24 hours of your trial period.

Here's the exact statement from Apple's website: "If you signed up for a free or discounted trial subscription and you don't want to renew it, cancel it at least 24 hours before the trial ends."

The payment processes on the App Store are exclusively managed by Apple. If you encounter any issues in this regard, please reach out to Apple for assistance.