New and existing licenses are present in the folder but when clicked on Add/Update licenses>Install licenses tab in Symantec Installation Manager (SIM) and browsed the folder, it does not show any file in Select License Files dialog box. No, .txt or .slf file can be browsed in this window There is no error message in logs.
In this case, the issue was due to non-English language selected in Control Panel>Region
Symantec Installation Manager 8.1.5228
Changed the language to English (US) from Control Panel\All Control Panel Items>Region and restarted the server. Now, the license file can be browsed and installed.