The form at https://www.apitest.io/request accepts (among others) the "url" parameter. This feature allows to reach internal services (like the OpenStack metadata server) or services running on loopback.
http://0x7f.1/ (nginx) => "If you see this page, the nginx web server is successfully installed and working. Further configuration is required."
http://169.254.169.254/meta-data (OpenStack metada) => directoty listing (instance-id, mac, local-ipv4, public-ipv4, network_config/content_path, SUBID, ipv6-addr, ipv6-prefix)
http://0x7f.1:8081/ (vestacp admin panel) => <a href="http://vestacp.com/">Powered by VESTA</a>
The metadata server does't seem to host any sensitive data. However, access to port 8081 may allow to reconfigure the OS or services (untested). Additional services may exist, but it seems that my IP address (126.96.36.199) was just blacklisted on your side.