'{
  "cartItem": {
    "sku": "f6e957d1-51b2-4a56-90be-dc3c877e3e3b",
    "qty": 1,
    "quote_id": "1234",
    "product_option": {
      "extension_attributes": {
        "custom_options": [
          {
            "option_id": "7818",
            "option_value": "file.jpg",
            "extension_attributes": {
              "file_info": {
                "base64_encoded_data": "/9j/4AAQSkZJRgABAQAAAQABAAD//gA7Q1JFQVRPUj ...",
                "type": "image/jpeg",
                "name": "file.jpg"
              }
            }
          },
          {
          "option_id": "7819",
          "option_value": "test"
          }
        ]
      }
    }
  }
}'