If you are already in the channel, the response is slightly different.
already_in_channel will be true, and a limited channel object will be
returned. This allows a client to see that the request to join GeNERaL is
the same as the channel #general that the user is already in:
This table lists the expected errors that this method could return.
However, other errors can be returned in the case where the service is down
or other unexpected factors affect processing. Callers should always
check the value of the ok params in the response.
Value passed for channel was invalid.
A channel cannot be created with the given name.
A team preference prevents the authenticated user from creating channels.
Value passed for name was empty.
Channel has been archived.
Value passed for name was empty.
Value passed for name contained only punctuation.
Value passed for name exceeded max length.
Value passed for name contained unallowed special characters or upper case characters.
Value passed for name was invalid.
No authentication token provided.
Invalid authentication token.
Authentication token is for a deleted user or team.
This method cannot be called by a bot user.
This method cannot be called by a restricted user or single channel guest.
The method was passed an argument whose name falls outside the bounds of accepted or expected values. This includes very long names and names with non-alphanumeric characters other than _. If you get this error, it is typically an indication that you have made a very malformed API call.
The method was passed a PHP-style array argument (e.g. with a name like foo). These are never valid with the Slack API.
The method was called via a POST request, but the charset specified in the Content-Type header was invalid. Valid charset names are: utf-8iso-8859-1.
The method was called via a POST request with Content-Typeapplication/x-www-form-urlencoded or multipart/form-data, but the form data was either missing or syntactically invalid.
The method was called via a POST request, but the specified Content-Type was invalid. Valid types are: application/x-www-form-urlencodedmultipart/form-datatext/plain.
The method was called via a POST request and included a data payload, but the request did not include a Content-Type header.
The team associated with your request is currently undergoing migration to an Enterprise Organization. Web API and other platform operations will be intermittently unavailable until the transition is complete.
The method was called via a POST request, but the POST data was either missing or truncated.
This table lists the expected warnings that this method will return.
However, other warnings can be returned in the case where the service
is experiencing unexpected trouble.
The method was called via a POST request, and recommended practice for the specified Content-Type is to include a charset parameter. However, no charset was present. Specifically, non-form-data content types (e.g. text/plain) are the ones for which charset is recommended.
The method was called via a POST request, and the specified Content-Type is not defined to understand the charset parameter. However, charset was in fact present. Specifically, form-data content types (e.g. multipart/form-data) are the ones for which charset is superfluous.