When you visit http://nowasp.local you see this error:
Warning: Detected PHP Curl is not installed on the server. This may cause issues detecting or downloading remote files. The server operating system seems to be Linux. You may be able to install with sudo apt-get install php[verion]-curl where [version] is the version of PHP installed. For example, apt-get install php7.2-curl if PHP 7.2 is installed.
I confirmed the remote file include exploit labs don't work until you:
$ sudo apt-get install php-curl
$ /etc/init.d/apache2 restart
Test fix worked:
Visit http://nowasp.local/index.php?page=http://example.com
and you should see remote site embedded within OWASP Mutillidae site.