Simple XML Sitemap IndexNow Verification key not available

Simple XML Sitemap IndexNow
Verification key not available
An IndexNow verification key needs to be generated and optionally added to settings.php in order for IndexNow engines to get notified about changes. This warning only applies to the production environment.

Go to: /admin/config/search/simplesitemap/search engines/settings

Generate verification key

The Generate verification key look like this:
The IndexNow verification key is defined in Drupal state:  '*************************************';

Copy it

Go to:

/sites/default/settings.php (put it in the last line)

paste sequence :

$settings['simple_sitemap_engines.index_now.key'] = '*************************************';
Note: Change  '*************************************'; with Generated verification key

Save.

Set at the file permission  settings.php to 0444