Module doesn't work

Conceptually this is a great addition to Group and much needed.
However, installed module and it doesn't work.
As per instructions, I also installed SMTP authentication support module (I tested that my installation of this module works, which it did).
I checked all of the boxes in the Group Notification config screen.
I performed the events that would trigger notifications and no notifications.

Additionally, after installing the module this message appears as related to the module config screen:
Warning: foreach() argument must be of type array|object, null given in Drupal\Core\Render\Element\Checkboxes::valueCallback() (line 113 of /home/site/public_html/site.com/web/core/lib/Drupal/Core/Render/Element/Checkboxes.php)