Just found your plugin, installed and activated, wanted to check post to see how the plugin was working and the following is displayed across the top of the front-end of the site…

Warning: Use of undefined constant newest_post_1link – assumed ‘newest_post_1link’ (this will throw an Error in a future version of PHP) in /home/vinta193/public_html/wp-content/plugins/add-newest-post-link-after-content/Add-newest-post-link-after-content.php on line 27