Axios call to complete Authorization Code Flow not working

[hometown]

Hello, 

I am working on a small project, and I am attempting to implement Authorization Code Flow Authentication. I am successfully obtaining the 'code', but my Axios call to obtain the access token is not working (400 error). I am sure it is because of the format of my Axios call, but I cannot find any good resources for how to do this  correctly (almost everybody does the Client Credential flow, which doesn't allow you to obtain user information, correct?). 

If anybody can give me advice on how to fix this code or otherwise accomplish user authentication so that I may obtain a Spotify user's top tracks, albums, etc, I would greatly appreciate it! 

Thanks.