You're seeing just the function mark, go back to Slack.Web.Groups module for more information.
Link to this function

mark(channel, ts, optional_params \\ %{})

View Source

Sets the read cursor in a private channel.

Required Params

  • channel - Private channel to set reading cursor in.
  • ts - Timestamp of the most recently seen message.

Errors the API can return:

  • channel_not_found - Value passed for channel was invalid.
  • invalid_timestamp - Value passed for timestamp was invalid.