client.lua

print('Script loaded')
function changeLivery(vehicle) -- Function to change the livery
        print('changeLivery function loaded')
        -- It changes the livery between the first one (0), to the 10th one (9)
        if livery < 9 then -- If the current livery is between 0 and 8 (we are still able to go further)
            livery = livery + 1 -- So we change to the next one
        else if livery == 9 then -- If the current livery is the last one (9)
            livery = 0 -- Since we can't change to the nexxt one (cause the next is 10, which does not exist), we change it back to 0 (first one)
        end

        SetVehicleLivery(vehicle, livery) -- Native function to set the livery of the vehicle to the above specified livery
        print('Livery should''ve been changed now')
        DisplayHelpText("~b~Livery ~g~Changed.") -- Success message

end

Citizen.CreateThread(function()
    while true do -- Loop that triggers the livery changer function
        print('The script is OK')
        Wait(0)
        ped = GetPlayerPed(-1)

        if IsPedInAnyVehicle(ped, false) then -- Only be able to change the livery if the player is in a vehicle
            print('Vehicle enter event TRIGGERED')
            vehicle = GetVehiclePedIsUsing(ped) -- Get the player vehicle's entity
            livery = GetVehicleLivery(vehicle) -- Current livery

            if IsControlJustPressed(1, 182) then -- If player presses the L key
                print('L key press event TRIGGERED')
                changeLivery(vehicle) -- The livery changer function gets triggered, on the player's vehicle
        else
            DisplayHelpText("~b~You must be in a vehicle in order to change your livery!") -- Error message
        end
    end
end)