What is the best way to make a group ranking bot nowadays?

I want to create a automatic group ranker for example when someone buys a gamepass the person gets ranked, what is the best way to accomplish this nowadays?

https://inventory.roblox.com/docs/index.html
https://groups.roblox.com/docs/index.html

Your best bet of making this would probably be using Noblox.

Just host a server on one of your computers.

Are there any already made repositories using that?

Just look it up, I had to do something similar before
https://devforum.roblox.com/t/how-could-i-make-a-game-similar-to-fe2cm/3055102