code: func (api *Client) SetChannelTopicContext(ctx context.Context, channelID, topic string) (string, error) {
  	values := url.Values{
  		"token":   {api.token},
  		"channel": {channelID},
  		"topic":   {topic},
  	}
  
  	response, err := api.channelRequest(ctx, "channels.setTopic", values)
  	if err != nil {
  		return "", err
  	}
  	return response.Topic, nil
  }
docs: // SetChannelTopicContext sets the channel topic and returns the topic that was successfully set with a custom context
  // see https://api.slack.com/methods/channels.setTopic