Upgrading to CS-Cart 4.21, safely.

What changed in 4.21 that affects add-ons

• PHP 7.4 to 8.3. 4.21.2 refuses to run below PHP 7.4 or on 8.4; 7.2 and 7.3 are no longer supported.
• Smarty 5 and Twig 3. Template plugins and filters moved; old custom template code that relied on the previous classes can break.
• Nova theme. New installs use the Nova storefront theme by default.
• New core features: product videos (YouTube, Vimeo), a pickup points service at checkout and a generated /llms.txt.
• Licensing plans decide which core features your edition can use.

Checklist before you upgrade

1. Make a copy. Clone the store to a staging host and upgrade the copy first.
2. Check PHP. Your server must run PHP 7.4 to 8.3 for 4.21.
3. Check add-ons. Ask each vendor whether their add-ons are tested on 4.21, and update them before the core.
4. Look for collisions. The Upgrade Center reports modified core files. Move customizations into add-ons, hooks and template overrides.
5. Set the admin e-mail. The Upgrade Center e-mails a restore link before it starts and will not run if it cannot send it.
6. Back up files and database, even though the Upgrade Center makes its own backup.

After the upgrade

• Clear the cache, then open the storefront in a private window.
• Place a test order with each payment and shipping method you use.
• Check your theme: custom Smarty plugins and overrides are the most common source of errors on 4.21.
• Check the vendor panel on Multi-Vendor: product editing, orders and payouts.
• Watch the error log for a few days.

Kavio Labs add-ons and themes tested up to 4.21.x

Every Kavio Labs add-on and theme on sale supports CS-Cart and Multi-Vendor from 4.17.2 up to 4.21.x and works through hooks and template overrides, with no core file changes. Each product page shows which builds were fully tested and which are supported.