Read More link not working 404

Hello I’m using the Umbra calendar theme and have created a test event. It works fine until the Read More is clicked. If so it then goes to 404 page not found.

I’ve looked at the actual event and tried to view there using the permalink and it also does not work saying page not found.

How can I fix this please?

Thanks

https://www.ads-software.com/plugins/all-in-one-event-calendar/