add WordPress script to page conditionally by category

is_single() doesn’t work for the page post type, use is_page() instead.

You’re also missing the first argument for wp_enqueue_script, the script handle. Source should be the second argument.

function my_conditional_enqueue_script1() {
    if ( is_page() && in_category( 19 ) ) { 
        wp_enqueue_script(
            'my-cart-script',
            '/members/application/cart/views/public/js/cart.js'
        );
    }
}
add_action('wp_enqueue_scripts', 'my_conditional_enqueue_script1');