After you make a purchase through the App Store, a confirmation email with your order information is sent to the Apple ID account you used.

If you didn't receive an email, you can find instructions on how to check your Apple purchase history here: http://support.apple.com/kb/HT2727

If you need to contact us for a purchase issue, please attach a screenshot of your Apple receipt. Make sure the name of the purchased item(s) and the date of purchase are clearly visible.

You can find instructions on how to take a screenshot on your Apple device here: https://support.apple.com/en-us/HT200289