If you get an error message you don't understand, google it.
A very quick google for "Keyerror" would have got you here: KeyError - Python Wiki
Which explains what causes the problem.
Now all you need to do is work out why - and since that requires your dtaa and yoru code running, we can't do that for you.
So, it's going to be up to you.
Fortunately, you have a tool available to you which will help you find out what is going on: the debugger. If you don't know how to use it then start here: pdb — The Python Debugger — Python 3.9.6 documentation
Put a breakpoint on the first line in the function, and run your code through the debugger. Then look at your code, and at your data and work out what should happen manually. Then single step each line checking that what you expected to happen is exactly what did. When it isn't, that's when you have a problem, and you can back-track (or run it again and look more closely) to find out why.
Sorry, but we can't do that for you - time for you to learn a new (and very, very useful) skill: debugging!