Include the featured image into RSS feed

wp-codesnippet-show-post-thumbnail-rss-feed.php

<?php
//add this code into your theme functions.php file

add_filter('the_content', 'tt_featured_image_in_rss_feed');

function tt_featured_image_in_rss_feed( $content ) {
 global $post;
 if( is_feed() ) {
   if ( has_post_thumbnail( $post->ID ) ){
     $prepend = '<div>' . get_the_post_thumbnail( $post->ID, 'medium', array( 'style' => 'margin-bottom: 10px;' ) ) . '</div>';
     $content = $prepend . $content;
   }
 }
 
 return $content;
}