Good evening John and welcome to the Events Calendar Support forum!
Thank you for reaching out to us.
We are sorry to hear about the challenges you have faced after purchasing Pro.
I would love to help you with this topic.
By the sound of it, I believe you will need to first download the Events Calendar Pro and install it on top of the Events Calendar free.
Once activated, you should get a spot to enter your Pro license key. Currently, there is only one for Event Aggregator on your install, hence the message.
I would recommend reading the following to guide you through this: https://theeventscalendar.com/knowledgebase/new-user-primer-the-events-calendar-and-events-calendar-pro/
Let me know how that goes.
Best regards,
Geoff B.