My spectate gui isn't working, while it should work fine, why?

I used these lines script it: I get the error on line 9, _G.gameplayers is defined in another script

cam = game.Workspace.CurrentCamera
local button = script.Parent:WaitForChild('Button')
local bar = script.Parent:WaitForChild('Bar')
local title = bar.Title
local prev = bar.Previous
local nextone = bar.Next

function get()
    for _, v in pairs(_G.gameplayers()) do
        if v.Name == title.Text then
            return(_)
        end
    end
end

local debounce = false
button.MouseButton1Click:connect(function()
    bar.Visible = true
    if debounce == false then
        debounce = true
        bar.Visible = true
        pcall(function()
            title.Text = game.Players:GetPlayerFromCharacter(cam.CameraSubject.Parent).Name
            script.Parent.Close.Visible = true
        end)
    elseif debounce == true then
        debounce = false
        pcall(function()
            cam.CameraSubject = game.Players.LocalPlayer.Character.Humanoid
        end)
        bar.Visible = false
    end
end)

prev.MouseButton1Click:connect(function()
    wait(0.1)
    local players = _G.gameplayers
    local num = get()
    local player = players[num-1]
    local playerr = players[#players]
    if not pcall(function()
        cam.CameraSubject = game:GetService('Players')[player].Character.Humanoid
    end) then
    cam.CameraSubject = game:GetService('Players')[playerr].Character.Humanoid

    end
    pcall(function()
        title.Text = game.Players:GetPlayerFromCharacter(cam.CameraSubject.Parent).Name
    end)
end)

nextone.MouseButton1Click:connect(function()
    wait(0.1)
    local players = _G.gameplayers
    local num = get()
    local player = players[num+1]
    local playerr = players[1]
    if not pcall(function()
        cam.CameraSubject = game:GetService('Players')[player].Character.Humanoid
    end) then
    cam.CameraSubject = game:GetService('Players')[playerr].Character.Humanoid

    end
    pcall(function()
        title.Text = game.Players:GetPlayersFromCharacter(cam.CameraSubject.Parent).Name
    end)
end)

Click this to see how my studio looks like