Hi there
Here is some more info.
You can see the error by registering for the event yourself via this link
https://leep.ngo/civicrm/?page=CiviCRM&q=civicrm%2Fevent%2Fregister&id=1332&reset=1
The error occurs after the confirmation screen.
I have attached a document with links to Stack Exchange where others are having similar problems in case that helps.
Also the full error backtrace provided by civicrm
Thanks for your help – happy to provide wp login if still needed