Do you think it's possible that there's a conflict with DT Register 4.2.9 and Gantry 5 templates? I upgraded this client's template from a Gantry 4 template to a Gantry 5 template. I can't imagine how it might be related, but between running PHP 7.4 for DT Register and using a Gantry 5 template, maybe there's an issue.
Does the beta release support PHP 8?
The client's event is September 19th. I've asked if they want to disable PayPal as a payment option, roll back their template to the previous Gantry 4 template, or take a chance by installing the beta version on a live site.
I don't really know a quick way to clone a website - I've downloaded websites and databases to create new sites, but that's very time-consuming.
I COULD install a copy of the website in a subdirectory that linked to the same database - does the update you provided make any changes to the database? If not, this might be an option. I could have the client send a customer to the subdirectory to register, and if it works, I can install the update on the live site and delete the subdirectory without sync issues with the database.
Thank you,
Ernie