Cart leads to page not found

We've been using EB for 5-years for registration for a conference but I'm running into an issue with setting up an event registration page this year. You can click on the Register button and it pops up the selected events and lets you choose the quantity of registrants as in past years. When clicking the checkout button it now tries going to a page url ending in /checkout and shows an error of "The requested page can't be found." I've looked through all the configuration settings and don't see anything that I think might cause this and I haven't changed any configuration settings since we used it last year so not sure what changed or how to resolve it so hopefully you can point me in the right direction.
I'm using event booking 4.5.1 on joomla 4.3.4
Thanks

Hi Don

There must be something special on your site causing the issue. Please submit a support ticket sending us super admin account of your site and link to the page which I can perform registration and see the error

We are going to check to see what's wrong and get it sorted

Regards,

Tuan