These following API links below are used for the New Group Ban API that you can add to your websites, discord bots, etc… to ban other players from your Roblox group.
Banning Users from a group:
https://groups.roblox.com/v1/groups/${groupId}/bans/${UserId}
Note: The above link is a POST request.
Unbanning Users from a group:
https://groups.roblox.com/v1/groups/${groupId}/bans/${UserId}
Note: The above link is a DELETE request.
Notice that both links are the same but one is a POST request and the other is a DELETE request.
Getting all group Bans:
https://groups.roblox.com/v1/groups/${groupId}/bans
This link allows you to view all the users that are banned from your group.
I hope this resource will help other developers that are using a third-party application for banning users from their Roblox groups. Group bans also ban Alt accounts as well.