Hi Brook,
Thank you for your help!
I went to WP-Admin > Events > Settings > Tickets, and clicked save.
I also enabled the Check payment gateway temporarily, checked out with that, and marked the order as paid, and everything worked perfectly.
I think the problem must be with the PayPal account. Can you provide any guidance for configuring PayPal Standard to work with Event Tickets Plus? Should I try enabling “Payment Data Transfer” and adding a PayPal identity token?
Best regards,
Clifton