Configuring Trusted Connection
Veeam ONE uses TLS to ensure secure data communication between Veeam ONE Web Client website and a web browser.
In case you installed a self-signed certificate, when you try to access Veeam ONE Web Client from a remote machine, the browser will display a warning notifying that the connection is untrusted (although it is secured with TLS).
To eliminate the warning, import the self-signed certificate to client machines (the machines from which you plan to access the Veeam ONE Web Client website).
For details on importing TLS certificates, see this Microsoft KB article.