With Slack's new granular permissions requirement, it is now necessary to first invite the EZ Notify bot in a private channel before that channel can receive notifications. 

Note that this is only required for private channels (has a lock icon) and not necessary for public channels (channels that start with the "#" sign).

To do so, just go to the private channel and send a message to @EZ Notify by Highview Apps. You should get a pop-up after hitting the enter key.  Click the "Invite to Channel" button to continue.