Adds a reaction to an item.

Required Params

• name - Reaction (emoji) name. ex: thumbsup

Optional Params

• channel - Channel where the message to add reaction to was posted.
• file - File to add reaction to.
• file_comment - File comment to add reaction to.
• timestamp - Timestamp of the message to add reaction to.

Errors the API can return:

• already_reacted - The specified item already has the user/reaction combination.
• bad_timestamp - Value passed for timestamp was invalid.
• file_comment_not_found - File comment specified by file_comment does not exist.
• file_not_found - File specified by file does not exist.
• invalid_name - Value passed for name was invalid.
• message_not_found - Message specified by channel and timestamp does not exist.
• no_item_specified - file, file_comment, or combination of channel and timestamp was not specified.
• too_many_emoji - The limit for distinct reactions (i.e emoji) on the item has been reached.
• too_many_reactions - The limit for reactions a person may add to the item has been reached.