Fretta open spawnmenu

[StandaxXx]

I am trying to make a spawnmenu for my gamemode in fretta, but I have a problem.

I am in the begining, so I didn't change the spawn menu yet. It should be giving weapons.
Problem is when i press Q i get lua error:

ERROR: GAMEMODE:'OnSpawnMenuOpen' Failed: gamemodes\constraintwars\gamemode\cl_init.lua:110: attempt to call method 'ShowSpawnMenu' (a nil value)

I am lua beginner so I don't know where to put the GM:ShowSpawnMenu() function.

Thanks for help.

cl_init.lua

function GM:OnSpawnMenuOpen()

    GAMEMODE:ShowSpawnMenu();

end

cl_gmchanger.lua

local SpawnMenu = nil



function GM:ShowSpawnMenu()

    if ( !IsValid( SpawnMenu ) ) then

        SpawnMenu = vgui.CreateFromTable( vgui_Splash )
        SpawnMenu:SetHeaderText( "Spawn Menu" )

        SpawnMenu:SetHoverText( "Buy props here." )

        local function = function() LocalPlayer():Give( "weapon_shotgun" ) end
        local Button = SpawnMenu:AddSelectButton( "Shotgun", function )
        Button.m_colBackground = Color(255, 90, 90, 255)

        local function2 = function() LocalPlayer():GiveAmmo( 30, "buckshot" ) end
        local Button2 = SpawnMenu:AddSelectButton( "Shotgun Ammo", function2 )
        Button2.m_colBackground = Color(255, 90, 90, 255)
 
        Button2.Think = function( self )
            self:SetDisabled( !LocalPlayer():HasWeapon( "weapon_shotgun" ) )
        end

        SpawnMenu:AddCancelButton()

    end

    SpawnMenu:MakePopup()

end