How to cancel a pending purchase?

You cannot, you have to wait for the charge to be made and then request a refund.

If this is a subscription then please read this link to learn "How to cancel a subscription from Apple" Click here --> https://support.apple.com/HT202039

Note:

• "If you don’t see Cancel Subscription, then the subscription is already canceled and won't renew." The "Expires" date means the current subscription will just run until then.

• Deleting an app does not cancel a subscription.

• If you don’t cancel trials more than 24 hours before your renewal date, your subscription might renew.

• If you don't have an Apple device, see the options near the very bottom of the support document

"If the subscription that you want to cancel is not listed", click here --> https://support.apple.com/HT212052

If you still can't find a subscription, contact Apple Support using the link at the end of the support article.

FOR REFUNDS for either a purchase or a subscription

click here to Report A Problem --> https://reportaproblem.apple.com/?s=6

Or click here --> https://support.apple.com/choose-country-region/media-services Select your country, then a product.

Realize Apple's terms of purchase for most countries are effectively, "All Transactions are final" (check terms at: https://www.apple.com/legal/internet-services/itunes/us/terms.html ). Apple does refund on a case by case basis, but they can also refuse.