A receipt from the App store is required for Customer Support to locate any missing purchases.
Below are links with instructions on how to find your purchase history.
When sending a receipt, please make sure it comes from directly from the App store and includes an order #, Amount, and Date/Time of the purchase.
Apple
Google Play
If you can not locate your purchase receipt, here's an extended tutorial on where to find it, depending on the merchant used for your purchase.
Google Play(Android users, purchasing from a phone or Tablet)
Device:
On your mobile device, open the Google Play Store app. Tap Menu Account to locate your 'Purchase History' section.
PC:
Visit http://wallet.google.com and log in with the same account used to make your purchase with. All purchases should be listed under Transactions. Select the purchase wich wasn't received.
OR
Visit http://payments.google.com and log in with the same account used to make your purchase with. On the left, click 'Subscriptions and services' and then 'View purchase'. Select an order to see your receipt.
You may visit Google Play Support for more information: https://support.google.com/googleplay/answer/2850369?hl=en
Apple App Store
Device:
Open your main settings and tap your Apple ID avatar. Click the 'Media&Purchase' option and scroll down to locate the 'Purchase History' section in order to display your purchase history and select the purchase which wasn't received.
PC:
On a computher with iTunes installed, click on 'account email' in the iTunes Store to access your account; you will be prompted to insert your Apple ID and password. Click 'Purchase History' to display your purchase history and select the purchase which wasn't received.
You may visit Apple Support for more information: https://support.apple.com/en-us/HT204088