mutation ReplyToGitLabDiscussion($input: GitLabDiscussionInput!, $body: String!) {
  replyToGitLabDiscussion(input: $input, body: $body) {
    id
    individualNote
    notes {
      id
      body
      author {
        id
        username
        name
        avatarUrl
        webUrl
      }
      createdAt
      updatedAt
      system
    }
  }
}

{
  "input": {
    "projectId": "id",
    "iid": 1,
    "discussionId": "id"
  },
  "body": "string"
}

{
  "data": {
    "replyToGitLabDiscussion": {
      "id": "id",
      "individualNote": true,
      "notes": [
        {
          "id": "id",
          "body": "string",
          "author": {
            "id": "id",
            "username": "string",
            "name": "string",
            "avatarUrl": "string",
            "webUrl": "string"
          },
          "createdAt": "string",
          "updatedAt": "string",
          "system": true
        }
      ]
    }
  }
}