HTTP ERROR 500

[patjk]

After installation, when I add:
wfLoadExtension( 'WikiSEO' );

I get this error:
This page isn’t working www.domain.com is currently unable to handle this request.
HTTP ERROR 500

I'm on PHP 7.2 and MW 1.31. How can I solve this?
Thanks.

[patjk]

PHP error log says:
root@host [/home/test/public_html/domain/wiki]# grep 07-Dec-2018 error_log|tail
[07-Dec-2018 10:46:32 UTC] PHP Fatal error: Uncaught Exception: /home/test/public_html/domain/wiki/extensions/WikiSEO/extension.json does not exist! in /home/test/public_html/domain/wiki/includes/registration/ExtensionRegistry.php:107