I have done exactly as you described below several times and get the same message:
Your Event Aggregator license key is invalid. Visit the Events Calendar website to check your licenses.
You suggest in your email below that I should put the key in Events, settings, licenses. The only place for me to add it is the Event Aggregator field.
Does it sound like I don’t have rights to do this? I am hooked up to a server for the hospital/med school.