CloudFlare (Full strict) Error 426

I am using CloudFlare Origin server SSL. I successfully installed CloudFlare Origin server SSL on CWPpro. But after select (Full (strict), i got error 426. When i select "Full" error is gone. i want to know what happening.
How to solved this problem.

CloudFlare is a whole other headache.

Support is so-so, and causes you to bang your head on the desk.

You understand that CF Origin Server SSL certs only apply to HTTPS services? It won't do you any good for other services such as mail. So on a CWP LAMP/LEMP server that usually provides mail and FTP it's pretty much a non-starter. Go with LetsEncrypt or get an inexpensive Comodo PositiveSSL certificate. (Speaking as one who has been down this road!)