Indent bulleted list via the API

Hi. I would like to automatically add a block to a WorkDoc that includes indentation. If I query an indented WorkDoc I get the following:

          {
            "id": "obfuscated",
            "type": "bulleted list",
            "content": "{\\"alignment\\":\\"left\\",\\"direction\\":\\"ltr\\",\\"deltaFormat\\":[{\\"insert\\":\\"Hello3\\"}],\\"indentation\\":2}"
          }

If I mirror the content back using the following GraphQL:

mutation ($doc_id: ID!, $content: JSON!) {
  create_doc_block(type: bulleted_list, doc_id: $doc_id, content: $content) {
    id
  }
}

{
  "content": "{\\"alignment\\":\\"left\\",\\"direction\\":\\"ltr\\",\\"deltaFormat\\":[{\\"insert\\":\\"Hello3\\"}],\\"indentation\\":2}",
  "doc_id": 12345
}

I get the following error:

  "error_data": [
    {
      "error_type": "Unrecognized property",
      "error_msg": "unrecognized property [indentation] in content"
    }
  ],

Why is it that indentation is fine for reading but not for writing. I did look at the Quill playground which seems to suggest I can add an indent value to the attributes object but that seems to get ignored by the API. So… is this possible at all?