Force Yoast SEO to only use Featured Image for og:image on singular

functions.php

<?php 
// Tell WordPress SEO to use only full featured image for og:image output... and nothing else on singular
function only_full_og_featured_image() {
  global $post;
  if ( is_singular() ) {
    if ( function_exists( 'has_post_thumbnail' ) && has_post_thumbnail( $post->ID ) ) {
      $featured_image_url = wp_get_attachment_image_src(get_post_thumbnail_ID( $post->ID ), 'full' );
      return $featured_image_url[0];
    }
  }
}
add_filter('wpseo_opengraph_image','only_full_og_featured_image');