Wordpress plugin to add a playlist after content not working at all...

I've used Pluginception to create a plugin to append a playlist containing attached music to a the_content of the current post by default. I'm struggling with making Easy Digital Downloads Frontend Submissions forms work for me, and this is a solution for the 80/20 issue (the 20% of features needed that require custom work!). ;)

Starting from a script from Pippin @Pippinsplugin - https://pippinsplugins.com/playing-nice-with-the-content-filter/ I wound up with the code below, but unfortunately it doesn't seem to work when run. It doesn't blow anything up either, which is good I suppose...

It's a relatively small, simple plug to do a simple task. But it doesn't work. :(

function download_show_playlist( $content ) { global $post; if( is_singular() && is_main_query() && $post->post_type === 'download' ) { $download = new EDD_Download( $post->ID ); $files = $download->get_files( ); $submission_attachment_ids = ''; if ( is_array( $files ) ){ $first = true; foreach ( $files as $key => $value ) { if ( !isset( $value[ 'attachment_id' ] ) ){ continue; } if ( $first ){ $submission_attachment_ids .= $value[ 'attachment_id' ]; $first = false; } else { $submission_attachment_ids .= ',' . $value[ 'attachment_id' ]; } } } else { return $content; // no files attached to the download }

        if ( !$submission_attachment_ids || strlen( $submission_attachment_ids ) < 1 ) {
            return $content; // no files attached to the download
        }

        $new_content = '[playlist ids="' . $submission_attachment_ids . '"]';
        $content .= $new_content;
    }   
    return $content;
}
add_filter( 'the_content', 'download_show_playlist' );