Default values for ACF flexible content fields

functions.php

<?php

  //Set a default layout to appear in a Flexible Content Field for certain post types (eg products)
  //We just set a default value for our desired field. This is an array of arrays. 
  //Each inner array requires at minimum an element called 'acf_fc_layout'. You may also set other field default values here (use field keys, not names).
  
  function mytheme_set_default_layout($value, $post_id, $field){

      if(get_post_type($post_id) == 'product' && empty($value)){
          $value = array(
              array( 'acf_fc_layout' => 'LAYOUT_NAME' /*, 'field_5dc07c52a036c' => 'field default value' */ ) 
          );
      }
      return $value;
  }
  add_filter('acf/load_value/name=FIELD_NAME', 'mytheme_set_default_layout',10,3);

?>