Good evening Arley and welcome back!
Thank you for reaching out to us.
We are sorry to hear about the error messages you have been getting while trying to purchase a ticket.
I would love to help you with this topic.
The first thing I would recommend is to go through our testing for conflicts procedure (preferably in a staging/dev environment or local install of your WordPress website) and let us know what you find out.
Basically the goal here is to revert back to a bare WordPress installation to see if the problem persists. It also allows us to pinpoint what the cause of the issue is.
And before I forget, please deactivate and clear wp-engine’s cache.
Also, I am noticing that you used to have the Wootickets plugin. Just to be sure, did you follow the following procedure to upgrade ?
Have a good week-end and let me know how it goes,
Geoff B.