Twitter Code Reedem?

Here you added the walkspeed as a Variable and you don't want to do that. I rewrote it a bit:

local plr=game.Players.LocalPlayer
local chr=plr.Character

box=script.Parent.TEXT
code=script.Parent.CODE
function clicked()
    if box.Text=="1337" then
        box.Text="Correct!"
        wait(2)
        box.Text="Code"
        chr.Humanoid.WalkSpeed=50
    else
        box.Text="nope"
        wait(2)
        box.Text="Code"
    end
end

code.MouseButton1Down:connect(clicked)

You can change the name of the Variables.

You need to check if a code was entered, so you need to change your function. Also, you used "=" twice on line 9, so you need to get rid of your "local b" and change game.Players to just plr since you explained what it was. You also need to check if the code was redeemed or not already, which you would wanna set a value to check.

local box = script.Parent.Parent.TextBox
local plr = script.Parent.Parent.Parent.Parent
local redeemed = false

box.FocusLost:connect(function()
    if box.Text == "1337" and redeemed == false then
        redeemed = true
        box.Text = "Code Accepted!"
        plr.Chracter.Humanoid.WalkSpeedSpeed = 50
        wait(1)
        box.Text = "Redeem Code"
    elseif box.Text == "1337" and redeemed == true then
        box.Text = "Already Used!"
        wait(1)
        box.Text = "Redeem Code"
    else
        box.Text = "Code Declined!"
        wait(1) 
        box.Text = "Redeem Code"
    end
end)

It is not referencing the player! Here is a fixed script.

local box = script.Parent.Parent.TextBox
local player = game.Players.LocalPlayer
function onClick()

    if box.Text == "1337" then
    box.Text = "Code Redeemed!"
    wait(2)
    box.Text = "Special Code"
    player.Humanoid.WalkSpeed = 50 
    else
    box.Text = "Wrong Code!"
    wait(2) 
    box.Text = "Special Code"


    end
end
    script.Parent.MouseButton1Click:connect(onClick)