How do I post a bulleted list using the slack api

The easiest workaround for this would be using '?' character itself in the text.

Slack also uses following as part of the block kit message to reflect bullet points:

"text": "? test",

"blocks": [
    {
      "type": "rich_text",
      "block_id": "erY",
      "elements": [
        {
          "type": "rich_text_list",
          "elements": [
            {
              "type": "rich_text_section",
              "elements": [
                {
                  "type": "text",
                  "text": "test"
                }
              ]
            }
          ],
          "style": "bullet",
          "indent": 0
        }
      ]
    }

Another reference:
https://superuser.com/questions/1282510/how-do-i-make-a-bullet-point-in-a-slack-message