To address the issue, do the following:

1. Open the IIS Manager (inetmgr) on which the Apex One server is installed.
2. Click Apex One server hostname.
3. Double-click on the IP and Domain Restrictions icon in the IIS section.
4. Check if the IP address is in the Deny Entry list. If exists, select the IP Address then click Remove.
5. Click on the Edit Feature Settings... in the Actions pane.
6. Check if the "Access for unspecified clients" is set to Allow.
7. Restart the IIS Admin Service.

If the issue persists, please contact Trend Micro Technical Support.