Help with creating long-lived token

I'm quite new to using the API, but I was successful once and trying to follow the same steps with no luck.  My issue is with trying to generate a long-lived token.  I am creating my new app, and getting my "App Key" and "App Secret".  I then generate an "Access Token".  From there, I use this

https://www.dropbox.com/oauth2/authorize?response_type=code&client_id=APP_KEY&redirect_uri=REDIRECT_URI  which then returns an "auth code" in the URL.  

Using that Auth Code I use the following:

curl -X POST "https://api.dropboxapi.com/oauth2/token" ^
-d code=AUTH_CODE ^
-d grant_type=authorization_code ^
-u APP_KEY:APP_SECRET

But every single time I get "{"error": "invalid_grant", "error_description": "redirect_uri mismatch"}" and not sure what I am doing wrong.