Block app from making purchase

If you subscribed to an app, the charges are authorized. If you subscribed to a trial subscription and didn't cancel the subscription 24 hours before the end of the trial and it converted to a paid subscription, the charges are authorized.

Managing auto-renewing subscriptions -

If you want to cancel a subscription from Apple - Apple Support

M1 Mac mini, macOS 14.1.2;  Watch, series 7 GPS/cellular, watchOS 10.1.1; iPad Pro 2nd Gen, iPadOS 17.1.2; iPhone 12 Pro, iOS 17.1.2; TV 4th Gen, tvOS 17; HomePods, audioOS 17.1.1 and Airport Express w/ Airplay 2

I keep getting unauthorized purchases from Roblox. It says there are no subscriptions. How do I prohibit purchases from this app?