/**
 * Prohibit a product category
 */
function custom_add_validation_rules_category() {

	if ( ! isset( WC()->cart ) ) {
		return;
	}

	$shipping_country      = WC()->customer->get_shipping_country();
	$shipping_state        = WC()->customer->get_shipping_state();
	$cart_contents         = WC()->cart->cart_contents;
	$cart_product_ids      = wp_list_pluck( $cart_contents, 'product_id' );
	$prohibited_categories = array( 34 ); // Add prohibited category IDs

	// Loop through each product to check if anyone has any prohitibited category
	foreach ( $cart_product_ids as $product_id ) {
		if ( array_intersect( wp_get_post_terms( $product_id, 'product_cat', array( 'fields' => 'ids' ) ), $prohibited_categories ) ) {
			wc_add_notice( __( 'There are some product (categories) in your cart that cannot be shipped to your location.' ), 'error' );
			break;
		}
	}

}
add_action( 'woocommerce_checkout_process', 'custom_add_validation_rules_category' );