Description This article describes the error: Web Page Blocked-Access
Denied for newly registered domain. Scope All FortiGate versions.
Solution If a domain name is not included in the database and the URL is
seen by the FDN server for the first time...
https://community.fortinet.com/t5/FortiGate/Technical-Tip-Rectifying-the-DUP-Ping-result-on-the-FortiGate/ta-p/336909
This article link is useful for troubleshooting DUP! error