This could be shown as a part if you have any
Firewall Rules enabled at your Cloudflare dashboard for your domain which is obviously blocking you from the access (based on the request).
Kindly, to check for any Firewall Rules navigate to Firewall Rules.
Therefore, navigate to Firewall events and check if you see your IP and others being blocked, if so.
Did you put the IPs in the
Firewall Rules with the action “Allow” and therefore in the
IP Access Rules with the same action?
Bot Fight Mode option being enabled?
Have you just in case, whitelisted your origin host / server IP too (in case of some HTTP requests, even wp-cron could be blocked, etc.)?
More about this error can be found at below articles: