Create a checkout session

Returns a `checkout_url` to redirect the customer to. A cart with one recurring product starts a subscription; otherwise it takes a one-time payment. Sessions expire after 24 hours. Use it whenever a customer is ready to pay: the card is collected on Utopia's own page, so your server never handles card details. Every item must be in the same currency (`MIXED_CURRENCIES` otherwise), a subscription cart holds that one recurring product and nothing else (`INVALID_CART`), and a saved product must be `active` (`PRODUCT_NOT_ACTIVE`) and priced above zero (`INVALID_PRICE`). List each product once and raise its `quantity` rather than repeating it. Items priced inline are always one-time. An expired session reads as `expired` and has no `checkout_url` left to send anyone to. Send `Idempotency-Key` so a retried request returns the first session instead of creating a second one. A test key sees only test-mode products and creates only test-mode sessions.

curl -X POST "https://example.com/checkout_sessions" \  -H "Content-Type: application/json" \  -d '{    "product_cart": [      {        "product_id": "pdt_3f2b8c1e9a4d4e7b8c2a1d5e6f7a8b9c",        "quantity": 1      }    ],    "customer": {      "email": "nour.alabbas@example.com",      "name": "Nour Al Abbas"    },    "return_url": "https://your-store.example/thank-you",    "metadata": {      "order_id": "1001"    }  }'

{  "object": "checkout_session",  "session_id": "cks_9b1e44a0c3d24f6e8a7b5c2d1e0f9a8b",  "kind": "payment",  "status": "open",  "checkout_url": "https://utopia-payments.com/checkout/cks_9b1e44a0c3d24f6e8a7b5c2d1e0f9a8b",  "total_amount": 34900,  "currency": "AED",  "product_cart": [    {      "product_id": "pdt_3f2b8c1e9a4d4e7b8c2a1d5e6f7a8b9c",      "name": "Pro course",      "quantity": 1,      "unit_amount": 34900    }  ],  "customer": {    "name": "Nour Al Abbas",    "email": "nour.alabbas@example.com",    "phone_number": null  },  "return_url": "https://your-store.example/thank-you",  "payment_id": null,  "subscription_id": null,  "metadata": {    "order_id": "1001"  },  "livemode": true,  "created_at": "2026-09-14T09:55:00.000Z",  "expires_at": "2026-09-15T09:55:00.000Z",  "completed_at": null}