When navigating to the Health Check page, I received a blank page and the following error message in my Apache error log:

[Mon Oct 05 21:03:46.078760 2020] [php7:error] [pid 7233] [client 70.114.131.253:55029] PHP Fatal error:  Uncaught Error: Call to undefined function curl_init() in /path/to/simplerisk/includes/healthcheck.php:599\nStack trace:\n#0 /path/to/simplerisk/includes/healthcheck.php(61): check_api_connectivity()\n#1 /path/to/simplerisk/admin/health_check.php(85): simplerisk_health_check()\n#2 {main}\n  thrown in /path/to/simplerisk/includes/healthcheck.php on line 599, referer: https://demo.simplerisk.com/admin/health_check.php

This error message means that PHP is trying to use curl to perform a health check of the various services that SimpleRisk uses, but the PHP Curl library is not installed.  To install it, run the following commands on your SimpleRisk instance as root:

Ubuntu:

sudo apt install php-curl

sudo service apache2 restart

RHEL/CentOS:

sudo yum install php-curl

sudo systemctl restart httpd

SUSE:

sudo zypper install php7-curl

sudo systemctl restart apache2