How would I detect player movment inside a part?

I am half asleep so I have no idea if this will work with multiple people.

So I put a server script inside of the desired part and a folder called PlayersOnPart

The script inside of the part

local Players = game:GetService("Players")
local Main = script.Parent

local Range = 40
local Check = true
local stop = 15


    local function balls()
    for _,Player in next, Players:GetPlayers() do
        local char = Player
        local name = char.Name
        if script.Parent.PlayersOnPart:FindFirstChild(name)then
            wait()
        elseif not script.Parent.PlayersOnPart:FindFirstChild(name) then
            local namedong = Instance.new("BoolValue",script.Parent.PlayersOnPart)
            namedong.Name = name
        end
        end
    end

local function noballs()
    for _,Player in next, Players:GetPlayers() do
        local char = Player
        local name = char.Name
        if script.Parent.PlayersOnPart:FindFirstChild(name) then
            script.Parent.PlayersOnPart:FindFirstChild(name):Remove()
        end
    end

end
    while wait() and Check do
        for _,Player in next, Players:GetPlayers() do
            local Char = Player.Character or Player.CharacterAdded:wait() 
            local HumanoidRootPart = Char:FindFirstChild('HumanoidRootPart')
            local A,B = HumanoidRootPart.Position, Main.Position

            local Dist = (A - B).Magnitude
            if stop >= Dist then
                balls()
            else
                noballs()           
        end
    end
end

if its confusing or if it doesn't work tell me tomorrow cause I'm so tired.

There is also a script inside of the workspace that gets the amount of players, I made it so it named the players inside of the part so if you wanna do anything with that go ahead, but here is the script for now.

local Folder = script.Parent.Part3.PlayersOnPart

while true do
    wait(1)
    print(#Folder:GetChildren())
end

Next time you ask a question try doing it yourself first or show some code of what you tried to do. Anyways gl with you game