I like it. Very straightforward and readable.

Very readable. I like your use of the list to make it clear and avoid all the indexing.

I first tried to code a recursive solution, but it kept coming back with some odd error about a left brace '{' and a JSON string or something. As I had no braces in my code and was not using any JSON, I figured it was some bug behind the scenes. So I used a less prefered set of loops.

Looking at some of the other solutions, I see there were even better options that would have required neither! Still, the frustration caused me to rate this as "Somewhat Satisfied" instead of my usual "Satisfied" rating.

This is written with god-awful switch statements because I had originally written it to accept input as a string and determine if it was a Roman Numberal or an integer, then convert it to the opposite. Still, I like all these dictonary and recursive algorithms I see here so much better than my own.

If you want to do it this way, how about using recursion?

It keeps telling me that I have not solved it when I try to look at the Solutions, but I have solved it. Twice. And both times successfully, passing all tests at all levels.

This solution is almost identical to mine! (I just finished mine.) You do not need to check if fifties < 0 though, because it never can be due to your 'if (fifties == 0)' statement.