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

set_topic(channel, topic, optional_params \\ %{})

View Source

Change the topic of a conversation. The calling user must be a member of the conversation. Not all conversation types may have a purpose set.

Required Params

  • channel - Conversation to set the purpose of. ex: G1234567890
  • topic - The new topic string. Does not support formatting or linkification. ex: Apply topically for best effects

Errors the API can return:

  • channel_not_found - Value passed for channel was invalid
  • is_archived - Channel has been archived
  • method_not_supported_for_channel_type - This type of conversation cannot be used with this method.
  • not_in_channel - Authenticated user is not in the channel.
  • too_long - Topic was longer than 250 characters.
  • user_is_restricted - This method cannot be called by a restricted user or single channel guest.