The Restrictions Passcode is independent of your unlock Passcode. This additional passcode is used to lock and prevent unauthorised changes to some system settings.
If you have forgotten the ScreenTime (a.k.a Restrictions) passcode, one of the two procedures outlined within this link should resolve the problem:
If you forgot your Screen Time passcode - Apple Support
If your iPad is capable of supporting iPadOS 13.x or later, you should update to the most current version before attempting to resolve a forgotten ScreenTime passcode. The most recent iPadOS updates have introduced a new mechanism whereby a forgotten ScreenTime passcode can be reset without wiping the iPad.
To reset a forgotten ScreenTime passcode on older versions of iOS/iPadOS, the iPad must be reset “as new”, losing all locally stored data. In this situation, you’ll not be able to restore your data from an iCloud or iTunes backup - as the forgotten passcode is integral to the backup.