How to check the visitors who left the checkout page without buying

If you’re using Woocommerce, google “Woocommerce abandoned cart plugin”. There are lots of solutions out there, like:

WooCommerce Cart Abandonment Recovery (100% free): https://wordpress.org/plugins/woo-cart-abandonment-recovery/

Abandoned Cart Lite for WooCommerce (free with paid upgrade): https://wordpress.org/plugins/woocommerce-abandoned-cart/

Abandoned Cart Recovery ($59, sold by Woocommerce.com): https://woocommerce.com/products/abandoned-cart-recovery/

Good luck!