My gift card balance dropped by more than the cost of the app I bought.

I bought an app for my Mac for $9.53. I had a gift card balance at the time of the purchase of over $30. After the purchase processed, my balance was $6.60. I checked purchase history to see if I was changed for something else (Apple Music, storage, something a family member purchased on our share plan...) and there was no other purchase history today.

Where's my money?