How to cancel a purchase that was accidentally made?

You can't not have paid for it. You have to pay for it and then ask for a refund.

Confirm you have canceled any subscription automatic renewal (if you simply delete an app this does not cancel subscriptions):

Review the information in this support article by clicking on the link to learn how to cancel a subscription from Apple. ➔ If you want to cancel a subscription from Apple - Apple Support If you subscribed to this in the EU from a third party, see: About purchases not billed through the App Store or the App Store's In-App Purchase system - Apple Support instead.

• "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."

• An existing subscription will normally continue until the end of its term and may then renew automatically. Stopping automatic renewal is effectively canceling it. "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. Note special conditions for some countries: About canceling subscriptions in Germany, Israel, South Africa, or Türkiye - Apple Support

• Read the article to see what to do about subscriptions that do not appear in your list. If you still can't find a subscription, contact Apple Support using the link at the end of the support article.

• Canceling a subscription does not automatically start a refund.

If you wish to pursue a refund, follow the directions in this support article about how to request a refund for apps or content that you bought from Apple ➔ Request a refund for apps or content that you bought from Apple - Apple Support

Read this support article for information about how long it takes to receive a refund (if one is granted), and how to check the status of a refund for apps or content that you bought from Apple --> Check the status of a refund for apps or content that you bought from Apple - Apple Support

Rainwalker87 Said:

"Cancel purchase: So, ive downloaded an app and it immediately threw a payment plan for something at my face, and ive accidentally agreed to the subscription, charging it to a card that has no funds. It's affecting my other subscriptions, and i would like to get rid of it, and still have not paid for it. Is there any way for me to fix it?"

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Ridding of a Purchase:

You need to request a refund. Note that the refund is not instantaneous. Meanwhile remove the app, by holding your finger on it, and the tapping the "X". Resulting a Refund: Request a Refund for Apps or Content that you Bought from Apple - Apple Support

How it is Affecting the Other Subscriptions?

See you subscriptions and cancel them here: View or Cancel App Subscriptions on iPhone - Apple Support

Note in what was said earlier in another post which might be a bit confusing. Getting rid of an app does not cancel a subscription. Getting rid of the app is just clean-up work.

The rest of the post basically duplicates what I said.