App purchased by mistake.

Hi HU63TE,

Welcome to the Apple Community.

Apple support have an article online to help you :)

Request a refund for apps or content that you bought from Apple

https://support.apple.com/en-au/HT204084

(Note: If the charge is pending, you canʼt request a refund yet. 

After the charge goes through, you can try to request a refund again.)

Hope this helps you :)