If you're looking at this website, you either looked through the patcher or the patched .exe, found this link by chance, or I just told you the link.
My servers support Newgrounds songs and NONG songs, including (due to a coding mistake, which turned into a feature) unwhitelisted NG songs.
For the official website, go to nong.kontroll.dev.
If you want to use my song servers in Geometry Dash, download the patcher here, run it with Geometry Dash closed, and then play like normal!
If you want to use my song servers for your own use, simply go to https://nong.7m.pl/songInfo.php, and in the url use "songID" as a query. (https://nong.7m.pl/songInfo.php?songID=661012)
The API supports both GET and POST requests, so use whichever you like!