CloudFlare works with HTTPS differently than cPanel. If you're using their proxied network, You need to enable the Universal SSL of Cloudflare and upload an origin certificate given by CloudFlare so that there is end-to-end encryption. AutoSSL can't work for CloudFlare-proxied networks because your site is pointing to 3 CloudFlare IP Addresses that do not belong to the Server.
You can use Cloudflare for DNS use by disabling the proxy network and then running AutoSSL. This will limit Cloudflare to their DNS and firewall only, and disable their CDN or Load Balancing.
You can also just change your name servers to ours until the SSL is installed. Then change it back to CloudFlare and the SSL will work until it's expired.
If you are using CloudFlare, you may want to consider getting a third-party SSL and adding it manually. Then you can keep track of when it will need to be updated again. You can also do SSL for two years if installed manually. Our partners that provide SSL are SSLCA and EZ Domain Name. We also provide third-party SSL certificates in your cPanel and from our shopping cart: