You're seeing just the function upload, go back to SlackWeb.Files module for more information.
Link to this function

upload(file, filename, optional_params \\ %{})

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Uploads or creates a file.

Required Params

  • file - File contents via multipart/form-data. ex: ...
  • filename - Filename of file. ex: foo.txt

Optional Params

  • channels - Comma-separated list of channel names or IDs where the file will be shared.
  • content - File contents via a POST var. ex: ...
  • filetype - Slack-internal file type identifier. ex: php
  • initial_comment - Initial comment to add to file. ex: Best!
  • title - Title of file. ex: My File

Errors the API can return:

  • invalid_channel - One or more channels supplied are invalid
  • posting_to_general_channel_denied - An admin has restricted posting to the #general channel.