Make line item quantities adjustable

curl https://api.stripe.com/v1/checkout/sessions \
  -u "
sk_test_BQokikJOvBiI2HlWgH4olfQ2
:" \
  -d "line_items[0][price_data][currency]"=usd \
  -d "line_items[0][price_data][product_data][name]"=T-shirt \
  -d "line_items[0][price_data][unit_amount]"=2000 \
  -d "line_items[0][price_data][tax_behavior]"=exclusive \
  -d "line_items[0][adjustable_quantity][enabled]"=true \
  -d "line_items[0][adjustable_quantity][minimum]"=1 \
  -d "line_items[0][adjustable_quantity][maximum]"=10 \
  -d "line_items[0][quantity]"=1 \
  -d "automatic_tax[enabled]"=true \
  -d mode=payment \
  --data-urlencode success_url="https://example.com/success" \
  --data-urlencode cancel_url="https://example.com/cancel"

# Set your secret key. Remember to switch to your live secret key in production!
# See your keys here: https://dashboard.stripe.com/apikeys
Stripe.api_key = 
"sk_test_BQokikJOvBiI2HlWgH4olfQ2"

require 'sinatra'

# You can find your endpoint's secret in your webhook settings
endpoint_secret = 'whsec_...'

post '/webhook' do
  event = nil

  # Verify webhook signature and extract the event
  # See https://stripe.com/docs/webhooks#verify-events for more information.
  begin
    sig_header = request.env['HTTP_STRIPE_SIGNATURE']
    payload = request.body.read
    event = Stripe::Webhook.construct_event(payload, sig_header, endpoint_secret)
  rescue JSON::ParserError => e
    # Invalid payload
    return status 400
  rescue Stripe::SignatureVerificationError => e
    # Invalid signature
    return status 400
  end

  if event['type'] == 'checkout.session.completed'
    checkout_session = event['data']['object']

    line_items = Stripe::Checkout::Session.list_line_items(checkout_session['id'], {limit: 100})

    # Fulfill the purchase...
    begin
      fulfill_order(checkout_session, line_items)
    rescue NotImplementedError => e
      return status 400
    end
  end

  status 200
end

def fulfill_order(checkout_session, line_items)
  # TODO: Remove error and implement...
  raise NotImplementedError.new(<<~MSG)
    Given the Checkout Session "#{checkout_session.id}" load your internal order from the database here.
    Then you can reconcile your order's quantities with the final line item quantity purchased. You can use `checkout_session.metadata` and `price.metadata` to store and later reference your internal order and item ids.
  MSG
end