<?php
// Do not copy opening php tag


function bb_auth_reply_view( $reply_id ) {
$reply_id = bbp_get_reply_id( $reply_id );

// Check if password is required
if ( post_password_required( $reply_id ) )
return get_the_password_form();

$content = get_post_field( 'post_content', $reply_id );

// first topic reply shouldn't be hiding
$rep_position = bbp_get_reply_position($reply_id);

// if user is not logged in and not the first post topic
if( !is_user_logged_in() && $rep_position > 1 ) {
    return "Replies only viewable for logged in users";
  } else {
    // return normal
    return $content;
  }
}
add_filter( 'bbp_get_reply_content', 'bb_auth_reply_view' );