Shopify Script - Free Shipping with purchase of a specific product

free-shipping-with-product.rb

# This is the product you need to buy to get free shipping
PRODUCT_ID = 000000000000
# This is the name of the shipping rate you want to discount (you can probably ad more options here and loop over them or soemthing
SHIPPING_NAME = "Standard Shipping"
# This is updated shipping name
UPDATED_SHIPPING_NAME = "FREE Standard Shipping"
# This is the message that will appear next to the doiscounted shipping rate option
MSG = "Buy X get Free Delivery offer"

is_in_cart = false

# Test if the item is in the cart
Input.cart.line_items.select do |line_item|
  product = line_item.variant.product
  if product.id == PRODUCT_ID
    is_in_cart = true
  end
end

# It is so make shipping free
if is_in_cart
  Input.shipping_rates.each do |shipping_rate|
    next unless shipping_rate.name == SHIPPING_NAME
      shipping_rate.change_name(UPDATED_SHIPPING_NAME, { message: "" })
      shipping_rate.apply_discount(shipping_rate.price, message: MSG)
  end
end

Hi, hope it’s going well. Do you know if this code is still working? Where would I install this script?

[Error] undefined method 'map' for nil
shopify/std_lib/cart_shipping_rates/output.rb:7:in #Class:0x7faad27081c0.to_hash
shopify/std_lib/core/script_kernel.rb:12:in Object.prepare_output

Gives error to me.