2 things I noticed: get_field()
isn’t specifying a post to get the field from, which is necessary outside the loop:
$add_description = get_field( 'body', $post->ID );`
And to set a post meta value you should use update_post_meta()
, not wp_update_post()
:
update_post_meta( $post->ID, '_aioseop_description', $add_description );