I can’t change the Screen time on my son’s ipad

I originally set up Screen time limits on my son’s iPad with a particular code, say 1234

Last week, I needed to give him the code because he needed more time & I was away. I figured I would change it later.

Now, I’m trying to change his screen time code and it’s proving impossible.

I was able to change his screen time limits from my iPhone and set a new code, say 4321.

BUT the old code 1234 is still the code that works directly on his iPad. And when he wants to “request more screen time”, he can easily grant himself all day access using the old code. The new code doesn’t work on it.

Please help!