Problem: The user was getting a fatal error from WooCommerce Blocks.
Solution: This error Call to undefined function mb_strtolower() means that the Multibyte String PHP extension(mbstring) is missing in your server.
Check with your hosting provider and ask to enable the Multibyte String extension. It is a Toolset requirement https://toolset.com/toolset-requirements/
If you are using cPanel or a similar hosting interface, you can enable it on the PHP extensions page.
This is the technical support forum for Toolset - a suite of plugins for developing WordPress sites without writing PHP.
Everyone can read this forum, but only Toolset clients can post in it. Toolset support works 6 days per week, 19 hours per day.