Enable 1 eligible discount code for Shopify Script Editor promo: Buy 4 items for $120

[lextui]

Hello, I plan to use Shopify Script Editor for a bundle promo. Currently it's customized so that customers can purchase 4 items for $120, but all discount codes are ineligible. How do I change the setting so only 1 existing code is eligible for this promo?

This code is included to exclude ALL discount codes. Is there a way to edit it?

# DisableDiscountCodesCampaign
#
# Any discount codes will be rejected with the entered message.
# ================================================================
class DisableDiscountCodesCampaign
  def initialize(rejection_message)
    @rejection_message = rejection_message
  end

  def run(cart)
    return if cart.discount_code.nil?

    cart.discount_code.reject(message: @rejection_message)
  end
end