For Event Notifications, you need two permissions on the monitorING server, for the service account running on the monitorED server. First, there's SQL. Second, there's Endpoint. It must have both.
If you just have CONNECT SQL enabled, not the endpoint, then what I saw in sys.transmission_queue was:
An error occurred while receiving data: '24(The program issued a command but the command length is incorrect.)'.
Here's the command to grant it. Remember that the authorization will be the name you're logged in as, so you might change that or ALTER the AUTHORIZATION afterwards (see http://thebakingdba.blogspot.com/2015/01/event-notifications-changing-security.html)
GRANT CONNECT ON ENDPOINT::[ENAudit_Endpoint] TO [yourdomain\monitorEDserviceacct]