A message or error that includes “missing client id” will be caused by either a new installation or a bug. When the Client ID (aka App ID) has not been entered by the administrator and someone attempts to use the Twitch Login feature or a number of other actions, this response will be giving by the Twitch API.
This is best done using the TwitchPress Setup Wizard which can be accessed through the WP Help tab when on any TwitchPress view. There is also a settings page where app credentials can be entered/updated quickly at anytime.
If this doesn’t appear to be the cause if your problem please report a possible bug and description the causing action as this API response can be caused by many things. That makes it difficult to pin-point the cause.