Finding the four digit passcode used by Screen Time.

I am trying to use Screen Time to allow me to purchase in-app offers. I previously blocked this option some years ago, but now want the option back. Screen Time is wanting a four digit passcode to do anything but my current phone uses six digits and I want to keep the six digit passcode for the phone. I did try changing the passcode for the iPhone to four digits, but was still blocked from getting into Screen Time. Help????