title: When attempting to update topic on slack channel, I get `method_not_supported_for_channel_type`
body: <p>I am using a bot to post some things to a slack channel. One of the things I need it to do is automatically update the channel's topic.</p>
  
  <p>According to the API documentation, this should do the trick: <code>https://slack.com/api/channels.setTopic</code> 
  <a href="https://api.slack.com/methods/channels.setTopic" rel="nofollow noreferrer">As per the docs</a>, I am passing in my token, channel id and topic. </p>
  
  <p>So the API request looks like this (not sure if relevant, but I'm doing it from postman):</p>
  
  <pre><code>POST /api/channels.setTopic HTTP/1.1
  Host: slack.com
  Content-Type: application/json
  cache-control: no-cache
  token=MY_BOT_USER_OAUTH_ACCESS_TOKEN
  channel=MY_CHANNEL_ID
  topic=Some topic
  </code></pre>
  
  <p>The response I am getting is:</p>
  
  <pre><code>{
      "ok": false,
      "error": "method_not_supported_for_channel_type"
  }
  </code></pre>
  
  <p>I can't seem to find anything about this. What does it mean?
  Not sure if worth noting, but I am attempting to do this in a private channel (that the bot is a part of).</p>
  
  <p>So am I missing something?</p>