Cloudflare is a good web service that provides CDN, Caching, HTML – JavaScript – CSS Minifying and also provides security from DDOS attacks at free of cost.
But use this service you have to add your domain to Cloudflare.
Interaction is simple at your dashboard’s top navigation bar there is a prominent button called ‘Add Site’, it transfers you to the next page where you can copy-paste your website’s URL.
If you are getting error like ‘Invalid Domain’ while adding your website to Cloudflare then use this trick to bypass this error.

IF you are copy-pasting URL with http suffix then you will get an error:
// You will get error http://yourdomain.com
Then you have to enter your domain without http or www, It should look like this:
// Success yourdomain.com
‘Invalid Domain’ error should be resolved by now.
Hope it helps.
Thanks & Regards
Mandar Apte