Hello, your app charged me $29.99, please explain what the charge is.

See the following Apple articles:

View your purchase history for the App Store, iTunes Store, and other Apple media services

View your purchase history for the App Store, iTunes Store, and other Apple media services - Apple Support

How apps, content, and subscriptions from Apple are billed

How apps, content, and subscriptions from Apple are billed - Apple Support

If you see an Apple Services charge you don't recognize on your Apple Card

If you see an Apple Services charge you don't recognize on your Apple Card - Apple Support

If you want to cancel a subscription from Apple

If you want to cancel a subscription from Apple - Apple Support

If the subscription that you want to cancel is not listed

If you want to cancel a subscription from Apple - Apple Support

If you see "apple.com/bill" on your billing statement

If you see "apple.com/bill" on your billing statement – Apple Support (UK)

If you see an unexpected charge

You can request a refund* for a purchase that you don't recognize, but you must pay for the purchase first. You can also cancel a subscription if you don't want to continue it.

*You must request the refund within the refund period. Refunds are not guaranteed. For more information, see the Terms & Conditions.

❗️Identify legitimate emails from the App Store or iTunes Store

Identify legitimate emails from the App Store or iTunes Store - Apple Support

Hello ~ Take a look here:

Subscriptions and Billing - Official Apple Support

If you cannot view the charge contact your banking institution and/or credit card company to ensure that your information has not been breached.

~Katana-San~