TextBox text returning nil

Hello, I’m trying to make a custom admin GUI. But the text value of the textbox returns to a nil value. I found this out by printing the second argument.
Local script:

local commandFrame = script.Parent.CommandFrame
local commandBox = commandFrame.MainBox
local UserInputService = game:GetService("UserInputService")
local prefix = "/"
local player = game.Players.LocalPlayer

commandFrame:TweenSize(UDim2.new(1,0,0,0),Enum.EasingDirection.InOut,Enum.EasingStyle.Quad,.5)

local function inputBegan(input,typing)
	if input.KeyCode == Enum.KeyCode.Semicolon then
		commandFrame:TweenSize(UDim2.new(1,0,0.1,0),Enum.EasingDirection.InOut,Enum.EasingStyle.Quad,.5)
		commandBox:CaptureFocus()
	end
end

local function focusLost(enterPressed)
	if enterPressed then
		local lowerText = commandBox.Text:lower()
		
		local text = lowerText:split(" ")
		local command = text[1]
		local splitCommand = command:split(prefix)
		local commandName = splitCommand[2]
		
		if commandName then
			local arguments = {}
			for i=2,#text,1 do
				table.insert(arguments,text[i])
			end

			game.ReplicatedStorage.FireCommand:FireServer(commandName,arguments)
		end
		commandFrame:TweenSize(UDim2.new(1,0,0,0),Enum.EasingDirection.InOut,Enum.EasingStyle.Quad,.5)
	end
end

UserInputService.InputBegan:Connect(inputBegan)
commandBox.FocusLost:Connect(focusLost)

Server script:

local commands = {}

local function findPlayer(target)
	for i,v in pairs(game.Players:GetPlayers()) do
		if v.Name:lower():sub(1,#target) == target:lower() then
			return v
		end
	end
	return nil
end

commands.kill = function(player,arguments)
	local target = arguments[2]
	if target then
		local plrTarget = findPlayer(target)
		
		if plrTarget then
			plrTarget.Character.Humanoid.Health = 0
		end
	end
end

game.ReplicatedStorage.FireCommand.OnServerEvent:Connect(function(player,commandName,arguments)
	print(player,commandName,arguments[2])
	if commands[commandName] then
		commands[commandName](player,arguments)
	end
end)

Arguments[2] prints as nil and the command doesn’t run.

write this instead

 local lowerText = string.lower(commandBox.Text)

still prints nilimage

I have tried this with only a local script and it seems to work fine. It’s just when I add in the RemoteEvent it prints nil.