Make line item quantities adjustable

Configure the Checkout Session so customers can adjust line item quantity during checkout.

Create a Checkout Session with `adjustable_quantity` enabled

Set adjustable_quantity on your line_items when creating a Checkout Session to enable your customers to update the quantity of an item during checkout.

You can customize the default settings for the minimum and maximum quantities allowed by setting adjustable_quantity.minimum and adjustable_quantity.maximum. By default, an item’s minimum quantity is 0 and the maximum quantity is 99.

If you use adjustable quantities, change your configuration so that it uses adjustable_quantity.maximum when creating the Checkout Session to reserve inventory quantity instead of the line_items quantity.

Checkout prevents the customer from removing an item if it is the only item remaining.

# 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_4eC39HqLyjWDarjtT1zdp7dc"

require 'json'
require 'sinatra'

post '/create-checkout-session' do
  session = Stripe::Checkout::Session.create({
    payment_method_types: ['card'],
    line_items: [{
      price: '{{PRICE_ID}}',
      adjustable_quantity: {
        enabled: true,
        minimum: 1,
        maximum: 10,
      },
      quantity: 1,
    }],
    mode: 'payment',
    success_url: 'https://example.com/success',
    cancel_url: 'https://example.com/cancel',
  })

  { id: session.id }.to_json
end

Handling completed transactions

After the payment completes, you can make a request for the finalized line items and their quantities. If your customer removes a line item, it is also removed from the line items response. See the Fulfillment guide to learn how to create an event handler to handle completed Checkout Sessions.

To test your event handler, install the Stripe CLI and use stripe listen --forward-to localhost:4242/webhook to forward events to your local server.

# 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_4eC39HqLyjWDarjtT1zdp7dc"

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/signatures 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

Make line item quantities adjustable

Create a Checkout Session with adjustable_quantity enabled

Handling completed transactions

Create a Checkout Session with `adjustable_quantity` enabled