Error after upgrade from 2.2.5 to 2.4.2

Using Softaculous in cPanel I made a full backup of the site and performed an upgrade with confirmation that the software was upgraded successfully. However the site was not working with Server error 500.
I restored the site from the backup but the site was still not opening with the error message:
PHP Fatal error:  Cannot declare class vmod, because the name is already in use in /home/user/public_html/includes/library/lib_vmod.inc.php on line 3

Please advise.

Best regards,
Janusz

Incompatible modifications is commonly the cause when having trouble after an upgrade. It is possible you still have some remains after restoring your backup. Substitute the entire folder with your backup. Restore the database to the backup.

Otherwise remove or disable any modifications. It seems like something is trying to load lib_vmod.inc.php twice. It should only be loaded once in app_header.inc.php.

Thank you Tim for the tip, I will try this.

It worked.

It looks like some additional files and folders were left from the failed upgrade.
After making the entire directory when Litecart was installed empty and then restoring the backup from before the upgrade I no longer get the error

PHP Fatal error:  Cannot declare class vmod, because the name is already in use in /home/user/public_html/includes/library/lib_vmod.inc.php on line 3

Good to hear you are on track again.
Do you know which upgrade patch that halted?

Not yet. I will try new upgrade soon.
Which PHP version do you recommend?

PHP 8.1 will work but I would recommend 8.0 which does not halt with a fatal error for strict variable types.