You must have a valid SSL Certificate set up on QUIC.cloud to use QUIC.
If QUIC.cloud is working properly, your site should be using QUIC.
You can use a browser extension to verify this, such as HTTP/2 and SPDY indicator for Google Chrome. It will show a green lightning bolt indicator, if your website is using QUIC.
Alternatively, you could use HTTP/3 Check to test your site to see if it’s using QUIC.
If QUIC is now working on your site, that means you have successfully started using QUIC.cloud!