When you manually upgrade Management and Security Server to version 12.3 or higher, you must install the rweb-client.war file to complete the upgrade.
To install rweb-client.war:
In your Reflection for the Web download location, open the install_manual\components directory.
Locate and copy rweb-client.war to this MSS webapps folder:
<MSS install directory>\server\web\webapps
The servlet runner will expand the war file and an rweb-client context will be created.
Start (or restart) the MSS Server.