code: func (api *Client) UnfurlMessage(channelID, timestamp string, unfurls map[string]Attachment, options ...MsgOption) (string, string, string, error) {
  	return api.SendMessageContext(context.Background(), channelID, MsgOptionUnfurl(timestamp, unfurls), MsgOptionCompose(options...))
  }
docs: // UnfurlMessage unfurls a message in a channel