I didn’t make this purchase

There are only 3 possibilities:

1. You downloaded the app, which authorized an in-app purchase.
2. Someone you share an Apple ID with downloaded the app, which authorized an in-app purchase.
3. Your Apple ID account was hacked, and the hacker downloaded the app which authorized an in-app purchase.

For 3 see—>If you think your Apple ID has been compromised - Apple Support

To report this to Apple use https://reportaproblem.apple.com

We don't know what "this purchase" is. See this link for help --> If you see "apple.com/bill" or an unfamiliar charge on your statement - Apple Support

Another possibility is that you took out a free trial subscription which has started charging. Many people seem to be unaware that most free trial subscriptions will turn into paid ones if they are not cancelled.

Your ID did.