Unable to create service item custom_dropdown with sections via API v2

I’m trying to create service catalog item custom_dropdown with sections via API v2
following Service Desk API for Developers | Freshservice but it has no examples or schema for sections object.

I was able to get it from json representation of other service item with dynamic sections that was created manually:

{
  "service_item": {
    ...
    "custom_fields": [
      {
        ...
        "field_type": "custom_dropdown",
        "field_options": {
            "isSection": "true",
          "displayed_to_requester": "true",
          "placeholder": ""
        },
        "choices": [
          [
            "Action1",
            "Action1"
          ],
          [
            "Action2",
            "Action2"
          ]
        ],
        "sections": [
          {
            "name": "Action1",
            "fields": [
              {
                ...
              },
              {
                ...
              }
            ]
          },
          {
            "name": "Action2",
            "fields": [
              {
                ...
              }
            ]
          }
        ]
      }
    ]
  }
}

When I’m doing POST request to API to create new service item with same choices and sections, it is successfull and item is created but sections are empty:
 

{
  "service_item": {
    ...
    "custom_fields": [
      {
        ...
        "field_type": "custom_dropdown",
        "field_options": {
            "isSection": "true",
          "displayed_to_requester": "true",
          "placeholder": ""
        },
        "choices": [
          [
            "Action1",
            "Action1"
          ],
          [
            "Action2",
            "Action2"
          ]
        ],
        "sections": []
      }
    ]
  }
}

 API documentation says that “custom_dropdown” is a supported custom_filed type but says nothing about sections

Why is it not accepting privided sections configuration? Is it possible?