There are two ways you can bypass Cloudflare's protection when monitoring your website. One way is to whitelist Site24x7's IP addresses in Cloudflare's Firewall tab. This will prevent Cloudflare's protection from triggering.
The other way is to configure the "Force IP addresses" field in your monitor with your server's actual IP address. Note that this will also bypass any other Cloudflare features enabled for that particular domain name which may cause your website to respond differently while monitoring.