```http
POST /checkouts HTTP/1.1
Host: api.uat.walleydev.com
Authorization: Bearer bXlVc2VybmFtZTpmN2E1ODA4MGQzZTk0M2VmNWYyMTZlMDE...
Content-Type: application/json

{
  ...,
  "cart": {
    "items": [
      {
        "id": "10001",
        "description": "A product description",
        "unitPrice": 5.0,
        "quantity": 1,
        "vat": 25.0,
        "requiresElectronicId": true,
        "sku": "1111-111-1111",
        "shipping": {
          "tags": ["session-cart-item-tag"],
          "unitWeight": 10,
          "dimensions": {
            "height": 10,
            "length": 10,
            "width": 10
          },
          "shippingInterval": {
            "startDate": "2024-01-01T00:00:00",
            "endDate": "2024-01-07T00:00:00",
            "alternatives": [
              {
                "name": "alternative-name",
                "shippingInterval": {
                  "startDate": "2024-01-01T00:00:00",
                  "endDate": "2024-01-07T00:00:00"
                }
              }
            ]
          }
        }
      }
    ]
  },
  ...,
  "shipping": {
    "tags": ["session-cart-tag"],
    "shipments": [
      {
        "tags": ["session-shipment-tag"],
        "id": "shipment-1",
        "contents": [
          {
            "quantity": 1,
            "sku": "1111-111-1111"
          }
        ]
      }
    ],
    "shippingInterval": {
      "startDate": "2024-01-01T00:00:00",
      "endDate": "2024-01-07T00:00:00",
      "alternatives": [
        {
          "name": "alternative-name",
          "shippingInterval": {
            "startDate": "2024-01-01T00:00:00",
            "endDate": "2024-01-07T00:00:00"
          }
        }
      ]
    }
  },  
  ...
}
```