In the WooCommerce order completion there is only one field for the street & house number. Unfortunately, it often happens that the user forgets exactly this house number. The following snippet checks if the mentioned field also contains a house number.
add_action('woocommerce_checkout_process', 'custom_validation_process'); function custom_validation_process() { global $woocommerce; if(isset($_POST['billing_address_1']) and $_POST['billing_address_1'] != '') { if (!preg_match('/([0-9]+)/Uis', $_POST['billing_address_1'])) { if(function_exists('wc_add_notice')) wc_add_notice( __('Haben Sie die Hausnummer bei der Straße vergessen?'), 'error' ); else $woocommerce->add_error( __('Haben Sie die Hausnummer bei der Straße vergessen?') ); } } if(isset($_POST['ship_to_different_address'])) { if(isset($_POST['shipping_address_1']) and $_POST['shipping_address_1'] != '') { if (!preg_match('/([0-9]+)/Uis', $_POST['shipping_address_1'])) { if(function_exists('wc_add_notice')) wc_add_notice( __('Haben Sie die Hausnummer bei der Straße vergessen?'), 'error' ); else $woocommerce->add_error( __('Haben Sie die Hausnummer bei der Straße vergessen?') ); } } } }