Unless you're planning to resolve the boundary layer and model separation (good luck...), you'd probably be better off using panel methods than NS. Look at XFoil or JavaFoil for available implementations.
There are three major families of procedurally-defined NACA airfoils -- four-digit like the 2412, five-digit like the 23012, and the 6-series like the 64A012.
It looks like this site only expects the four-digit form, and is mis-parsing anything other than that -- which is a pity, because one of the uses of a tool like this is to get a sense of /why/ the 23012 is similar CLmax to the 2412, but with lower moment and a more sudden stall. If nothing else, input validation is necessary!
If the goal is to allow a user to compare the properties of different airfoils, there's a lot to get right to make sure they actually know what airfoils they're comparing. The alternative is to allow airfoil selection from one of these sites [1][2], which also allow a link to provide comparative analysis.
[1] https://m-selig.ae.illinois.edu/ads/coord_database.html [2] https://bigfoil.com/