I’m not here to help with scripting but just to let you know, my almost-three-year-old response is not correct.
A singular Google search can give you:
(Is It Against ToS To Sell Ranks & Have a Holder?)
Also, there’s lots of things that could go wrong with this.
PSA: Stop using Roblox proxies! (roproxy, rprxy.xyz, rprxy) - Resources / Community Resources - DevForum | Roblox
To put it short, do not sell group ranks as gamepasses. It’s unethical, and against Roblox’s rules.
It’s more worth it to make a good game, than making incredibly overpriced group rank gamepasses to make money as you could get in trouble.
Good luck!