Hey devs :)
if you use GODOT, it will also work!
I didn't find tutorials online, so I decided to make one. Here you can find the gist: Simple leaderboard in Godot
I will be working on the devlog soon, please let me know in the comments for gist what you want to see in it :)
Also, if you want to secure your leaderboard in Unity to verify that the entries are coming from the game itself and not from POST requests, I've made a devlog describing exactly that:
Hacking Leaderboard like a PRO
P.S.
Absolutely love this tool :)