PaymentRequest: id プロパティ

const details = {
  id: "super-store-order-123-12312",
  total: {
    label: "Total due",
    amount: { currency: "USD", value: "65.00" },
  },
};
const request = new PaymentRequest(methodData, details);
console.log(request.id); // super-store-order-123-12312

const response = await request.show();
console.log(response.requestId === request.id);

// And in serialized form too
const json = response.toJSON();
console.log(json.requestId, response.requestId, request.id);