WooCommerce make order notes or order comments required https://njengah.com/make-woocommerce-order-comments-required/

make_WooCommerce_order_comments_required.php

 <?php 
  
 /**
   *  Code Snippet should be added to the functions.php to make WooCommerce order comments required 
   */ 
   
  add_action('woocommerce_after_checkout_validation', 'njengah_make_woocommerce_order_comments_required');

  function njengah_make_woocommerce_order_comments_required() {
  
            // Check if order comments are set, if its not set add an error.
			
            if ( ! $_POST['order_comments'] )
			
                
        wc_add_notice( __( 'Please add delivery instructions' ), 'error' );
  }