We don’t charge our customers in their trial period.
If you downloaded the app from the App Store, Apple can charge your card before the trial period is over. That’s because Apple’s policy can override our pricing policy.
Apple's subscription policy defines that if a subscription it's not canceled 24 hours before the last day of the trial, Apple might charge you.
Please refer to the Apple Support help article here to learn more about this: https://support.apple.com/en-us/HT204084