I'm on Joomla 3.19.13 with CiviCRM 5.18.2 and using the Stripe Payment Processor 6.2.2.
This seems to be a problem popping up on Wordpress sites (https://civicrm.stackexchange.com/search?q=Could+not+find+valid+value+for+id) but I'm on a Joomla system. My problem seems most similar to this one -- but in my case the registration DOES NOT come through, but the credit card payment DOES go through the Stripe processor, without email, address, name, etc. Nightmare!
Even worse, this seems to be an intermittent problem. We've just opened this event registration a few days ago, and so far we have 20 successful registrations with payments processed as they should be. But 1 payment has gone through successfully without any registration data or identifying data in Stripe, and 6 or 7 of these "unknown" Stripe payments appear to be stuck in the "Uncaptured" stage in the Stripe system.
I've found multiple instances in the CiviCRM logs like this:
Nov 30 23:13:41 [error] $Fatal Error Details = Array ( [message] => Could not find valid value for id [code] => )
Tail end of backtrace like this:
Nov 30 23:13:41 [debug] $backTrace = #0 /home/fawcoho/public_html/administrator/components/com_civicrm/civicrm/CRM/Core/Error.php(385): CRM_Core_Error::backtrace("backTrace", TRUE) -1 /home/fawcoho/public_html/administrator/components/com_civicrm/civicrm/CRM/Utils/Request.php(121): CRM_Core_Error::fatal("Could not find valid value for id") -2 /home/fawcoho/public_html/administrator/components/com_civicrm/civicrm/CRM/Event/StateMachine/Registration.php(52): CRM_Utils_Request::retrieve("id", "Positive", Object(CRM_Event_Controller_Registration), TRUE)
Any troubleshooting ideas welcome -- Stripe has already confirmed that for these incorrect payments they are receiving the credit card info (number, expiry, CVC) but not any other identifying information.