Sometimes the Apple App Store hiccups and errors like this are reported.
We've found the best way to fix this is to restart your device and then try again. If you think the purchase may have happened, you can choose "Restore Purchases" from the bottom of the main page. You'll know for sure if you get a receipt from Apple. If not, then chances are it did not go through. You can also check your purchase history as described by Apple here:
https://support.apple.com/en-us/HT204088
We've found the best way to fix this is to restart your device and then try again. If you think the purchase may have happened, you can choose "Restore Purchases" from the bottom of the main page. You'll know for sure if you get a receipt from Apple. If not, then chances are it did not go through. You can also check your purchase history as described by Apple here:
https://support.apple.com/en-us/HT204088
(For security reasons, no Apple app developer has access to any customer information at all, so we're not able to tell you, or we would to save you the hassle!)
Happy puzzling!