How to fix these errors on page

Hello there

I have got some errors but I don't know what's a problems there.

This is a errors from error.log and on page.

Stack trace:
#0 /home/u691934333/domains/site/public_html/includes/library/lib_route.inc.php(122): include()
#1 /home/u691934333/domains/site/public_html/index.php(40): route::process()
#2 {main}
  thrown in /home/u691934333/domains/site/public_html/pages/ajax/checkout_customer.inc.php on line 192
[05-Mar-2023 17:02:10 Europe/Stockholm] PHP Fatal error:  Uncaught Error: Call to undefined method database::create_variable() in /home/u691934333/domains/site/public_html/includes/entities/ent_order.inc.php:67
Stack trace:
#0 /home/u691934333/domains/site/public_html/includes/entities/ent_order.inc.php(12): ent_order->reset()
#1 /home/u691934333/domains/site/public_html/pages/ajax/checkout_summary.inc.php(16): ent_order->__construct()
#2 /home/u691934333/domains/site/public_html/includes/library/lib_route.inc.php(122): include('/home/u69193433...')
#3 /home/u691934333/domains/site/public_html/index.php(40): route::process()
#4 {main}
  thrown in /home/u691934333/domains/site/public_html/includes/entities/ent_order.inc.php on line 67
[05-Mar-2023 17:07:38 Europe/Stockholm] PHP Fatal error:  Uncaught Error: Call to a member function validate() on null in /home/u691934333/domains/site/public_html/pages/ajax/checkout_customer.inc.php:192
Stack trace:
#0 /home/u691934333/domains/site/public_html/includes/library/lib_route.inc.php(122): include()
#1 /home/u691934333/domains/site/public_html/index.php(40): route::process()
#2 {main}
  thrown in /home/u691934333/domains/site/public_html/pages/ajax/checkout_customer.inc.php on line 192

checkout_customer.inc.php line 192 does not exist. What verison of LiteCart is this?

database::create_variable() is part of newer versions of LiteCart. This could inidcate you have some newer code in an older platform. Older some older components in a newer platform.

It is migrated to new version. I did it manually maybe that’s why some codes have not migrated or forgotten to migrate.

How can I fix them ?

It’s updated to 2.4.4. It was 2.1 or 2.2

[quote]I did it manually[/quote]
I think the answer is right there. You updated some components and some not. And now you have a mix of new and old not wanting to work together.

Here is what I think you should do.

1. Clone the production platform into an identical development platform.
2. Upgrade the development platform to 2.5.2.
3. Use a folder comparison software like WinMerge to compare the two platforms with eachother.
4. Transfer your mods line by line from production to the development.
5. Make sure everything is fine.
6. Upgrade the production platform.
7. Copy your modified files from development to production.

Other than that here is some good reading:
https://wiki.litecart.net/how_to_prevent_losing_changes_before_upgrade

Great, Thank you.