```http
PUT /checkouts/1eec44b5-66d3-4058-a31f-3444229fb727 HTTP/1.1
Host: api.uat.walleydev.com
Authorization: Bearer bXlVc2VybmFtZTpmN2E1ODA4MGQzZTk0M2VmNWYyMTZlMDE...
Content-Type: application/json

{
  "cart": [
    {
      "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"
              }
            }
          ]
        }
      }
    },
    {
      "id": "10002",
      "description": "Item two",
      "unitPrice": 2.0,
      "quantity": 1,
      "vat": 25.0,
      "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"
            }
          ]
        },
        {
          "tags": ["session-shipment-tag"],
          "id": "shipment-2",
          "contents": [
            {
              "quantity": 1,
              "sku": "10002"
            }
          ]
        }
    ],
    "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"
          }
        }
      ]
    }
  }
}
```