Why doesnt it accept fiddle if it is a possible translation? Is the meaning that different?
Just like in english they are two seperate things. The fiddle is a "mode" of the violin. Saying "I have not played the Fiddle" doesn't mean you haven't played the Violin.
It's hard to endorse your alternative sentence if you don't write it completely, but "I did not play the fiddle" should be accepted, and reported if not.
This interpretation is inaccurate to my ears. I HAVE not PLAYED the violin vs I DID not PLAY the violin. Yet Google translate, and apparently Duo thinks they are the same thing. Am I wrong?
I'm not sure what your question is.
The German sentence Ich habe die Geige nicht gespielt can be translated as either "I have not played the violin" or "I did not play the violin" -- German uses its tenses differently from English.