Thats dont add players always says no one in that group my config file:

{
  "Group Setup": [
    {
      "Oxide": "steam",
      "Steam": "https://steamcommunity.com/groups/hexagonrust"
    }
  ],
  "Update Interval in seconds": 300,
  "Log member changes to console": true,
  "Log member changes to file": true
}

Don't use the group URL, only the group name from the URL.

Thank you :))