v9.0.0

Major version release - The migration guide contains a detailed list of backwards-incompatible changes with upgrade instructions.
(⚠️ = breaking changes):

• ⚠️#1336 feat(http-client): retry closed connection errors
• #1415 #1417 API Updates
  • ⚠️ Replace the legacy Order API with the new Order API.
    • Resource modified: Order.
    • New methods: cancel, list_line_items, reopen, and submit
    • Removed methods: pay and return_order
    • Removed resources: OrderItem and OrderReturn
    • Removed references from other resources: Charge.order
  • Add support for amount_discount, amount_tax, and product on LineItem
  • Change type of Charge.shipping.name, Checkout.Session.shipping.name, Customer.shipping.name, Invoice.customer_shipping.name, PaymentIntent.shipping.name, ShippingDetails.name, and Source.source_order.shipping.name from nullable(string) to string

See the changelog for more details.