Following the above article, this error would mean that there is a CNAME record that is set to Cloudflare and that CNAME points to another URL domain which is already using Cloudflare.
Here are my suggestions regarding the various methods on how can I fix it:
To allow CNAME record resolution to a domain in a different Cloudflare account, the domain owner of the CNAME target must contact Cloudflare Support and specify the domains allowed to CNAME to their target domain. Once the owner of the account in question confirms that they are aware of the security risk and notifies the Support team that they are willing to proceed, the engineering team will manually lift the restriction.
A Cloudflare Pro, Business, or Enterprise plan is required on the target domain for Cloudflare Support to change default CNAME restrictions.
You could try disabling Cloudflare proxy for that particular CNAME record by switching from to (DNS-only)
Instead of setting a CNAME record, you could can add A record by specifying the IP address.
This might also be a DNS propagation issue, so you could check if the domain resolves correctly on the networks.
I got returned the Error 1016. Kindly, see below articles: