Why won't this admin check work?

game.Workspace.ChildAdded:connect(function(cp)
    for _,v in pairs(HAdmin) do 
        player = game.Players:GetPlayerFromCharacter(cp)
        if  cp.Name == v then
            wait()
            player.PlayerGui.Holo.OpenClose.Visible = true
        end
        if cp:IsInGroup(GroupId) and cp:GetRankInGroup(GroupId) >= GroupRank then
            repeat wait(0.1) until cp.PlayerGui
            cp.PlayerGui.Holo.OpenClose.Visible = true
        end
    end
end)

On line 8 I get the error IsInGroup is not a valid member of Part