Universal Commerce Protocol

// Create a checkout session via UCP
const response = await fetch(
  'https://ucp.stateset.io/api/checkout-sessions',
  {
    method: 'POST',
    headers: {
      'Content-Type': 'application/json',
      'UCP-Agent': 'profile="https://myapp.com/profile"',
      'Request-Id': crypto.randomUUID(),
      'Request-Signature': '<jws-detached-signature>'
    },
    body: JSON.stringify({
      line_items: [
        { item: { id: 'item_123' }, quantity: 2 }
      ],
      currency: 'USD',
      buyer: {
        email: 'buyer@example.com',
        first_name: 'John',
        last_name: 'Doe'
      },
      payment: {
        selected_instrument_id: 'pi_demo',
        instruments: [{
          id: 'pi_demo',
          type: 'card'
        }]
      },
      fulfillment: {
        methods: [{
          type: 'shipping',
          destinations: [{
            id: 'dest_1',
            street_address: '123 Main St',
            city: 'San Francisco',
            state: 'CA',
            postal_code: '94102'
          }],
          selected_destination_id: 'dest_1'
        }]
      },
      discounts: {
        codes: ['SAVE10']
      }
    })
  }
);

const checkout = await response.json();
// { id: "chk_xxx", status: "ready_for_complete", ... }