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

open(user, optional_params \\ %{})

View Source

Opens a direct message channel.

Required Params

  • user - User to open a direct message channel with.

Errors the API can return:

  • user_disabled - The user has been disabled.
  • user_not_found - Value passed for user was invalid.
  • user_not_visible - The calling user is restricted from seeing the requested user.