You are specifcally submiting these links to the search engine to index them within your sitemap.
The searchengine has already indexed them with other URLs.
Now these links link to the same content. Therefore the SEO URL is a duplicate so you have to specify that in your sitemap.
Canonical is the tag you give the prefered link for duplicate content. so in this example you would add the canonical tag so the search engine knows that this content of the duplicate URLS is your prefered one.
You can also redirect 301 or set a noindex for the "wrong" urls you dont want to be indexed.
Here is the google description and how to resolve it