Good evening Robert and welcome to the Events Calendar Support forum!
Thank you for reaching out to us.
I would love to help you with this topic.
I have the event calendar PRO installed on there for ONLY ONE SITE – their main magazine. They are not going to be using it on the other sites. Or if they do, it would only be a feed coming from the main site.
Do I have to buy the multisite license? $349 is a bit steep since I’m not using multisite to provide websites for unlimited clients / etc…
The short answer is no. You don’t need to be a multi-site license if you are not going to be using the Events Calendar Pro on more than one of these sites.
I would recommend reading the following article on that subject: https://theeventscalendar.com/knowledgebase/multisite-license/
Let me know if that helps.
Have a great day!
Geoff B.