Remote function giving a weird error?

This is my first time using remote functions and I'm very confused. I'm trying to make a mod panel for my game in which you can set a player's speed.

My script:

local DSS = game:GetService("DataStoreService")
local SpeedStore = DSS:GetDataStore("SpeedStore")

game.ReplicatedStorage.ModPanelRemoteFunction.OnServerInvoke:Connect(function(sender, player, value, _type) -- Where the error is
    if sender:GetRankInGroup(6323488) >= 2 then
        if _type then
            if _type == "Name" then
                game.Players:FindFirstChild(player):WaitForChild("leaderstats"):WaitForChild("Speed").Value = value
                return true
            elseif _type == "Id" then
                game.Players:GetPlayerByUserId(player):WaitForChild("leaderstats"):WaitForChild("Speed").Value = value
                return true
            end
        elseif not _type then
            local key = player
            local data 

            local s, eM = pcall(function()
                data = SpeedStore:GetAsync(key)
            end)

            if s and data then
                local s2, eM2 = pcall(function()
                    SpeedStore:SetAsync(key, value)
                end)

                return true
            elseif not data then
                return false
            end
        end
    else
        sender:Kick("gg") -- Anti-Exploit
    end
end)

My local script:

local playerGui = game.Players.LocalPlayer:WaitForChild("PlayerGui")
local playerText = playerGui.ModPanel.MainFrame.NameOrUserId.Text
local newValue = playerGui.ModPanel.MainFrame.NewValue.Text

script.Parent.MouseButton1Click:Connect(function()
    if game.Players:FindFirstChild(playerText) then
        local completed = game.ReplicatedStorage.ModPanelRemoteFunction:InvokeServer(game.Players.LocalPlayer, playerText, newValue, "Name")
        if not completed then
            output(playerText.." is not a valid username.")
        else
            output("Sucessfully changed speed.")
        end
        local _, _ = pcall(function()
            if game.Players:GetPlayerByUserId(playerText) then
                local completed = game.ReplicatedStorage.ModPanelRemoteFunction:InvokeServer(game.Players.LocalPlayer, playerText, newValue, "Id")
                if not completed then
                output(playerText.." is not a valid User Id.")
                else
                output("Sucessfully changed speed.")
                end
            else
                local completed = game.ReplicatedStorage.ModPanelRemoteFunction:InvokeServer(game.Players.LocalPlayer, playerText, newValue, nil)
                if not completed then
                    output(playerText.." is not a valid User Id")
                else
                    output("Sucessfully changed speed.")
                end
            end
        end)
    end
end)

function output(text)
    if playerGui.ModPanel.OutputFrame.Visible == false then
        playerGui.ModPanel.OutputFrame.Visible = true
        playerGui.ModPanel.OutputFrame.TextLabel.Text = text

        playerGui.ModPanel.OutputFrame:TweenPosition(
            UDim2.new(0.338, 0,0.083, 0),
            "Out",
            "Elastic",
            1)
    else
        playerGui.ModPanel.OutputFrame.TextLabel.Text = text
    end
end

The output:

OnServerInvoke is a callback member of RemoteFunction; you can only set the callback value, get is not available

If you are able to help me I would greatly appreciate it.