Not compatible with WooCommerce High-Performance Order Storage

WooCommerce has introduced a new storage model for orders called High-Performance Order Storage. It will reduce order creation from at least 50 queries to just 3. Unfortunately, this plugin is not compatible with HPOS.

To make the plugin compatible with HPOS you need to use the WC-specific CRUD classes and instead of accessing wp_postmeta directly. And compatibility must be declared.

There is a guide on how to upgrade to HPOS: https://github.com/woocommerce/woocommerce/wiki/High-Performance-Order-Storage-Upgrade-Recipe-Book