Please edit your wp-config.php and move the line define( ‘SUNRISE’, ‘on’ );

Wordpress MU Domain Mapping Version 0.5.5.1
Wordpress Version 4.7.3

When I visit /wp-admin/network/settings.php?page=dm_admin_page, I see the message:

Please edit your /home/username/public_html/wp-config.php and move the line define( ‘SUNRISE’, ‘on’ ); above the last require_once() in that file or make sure you updated sunrise.php.

I have done both these things:

• In wp-config.php, I have:

  /** Sets up WordPress vars and included files. */
  define('SUNRISE', 'on');
  require_once(ABSPATH . 'wp-settings.php');

• I have copied /wp-content/plugins/wordpress-mu-domain-mapping/sunrise.php to /wp-content/sunrise.php

yet the same error remains.

Help appreciated.

Regards,
Steve