External Agent Managers (FglAM) would not connect to Foglight Management Server (FMS) and below errors were seen in the FglAM logs.
Although FglAM was configured to use HTTP protocol to connect to FMS from the debug logs it was seen that FglAM was trying to connect to FMS via HTTPS protocol and evidently there were no certificated configured on either side to make a successful HTTPS connection.
The server.config file of the FMS has the below parameter set to TRUE.
Make sure that the "server.console.httpsonly" parameter was set to "FALSE" in the $FMS_HOME/config/server.config file of FMS which allowed external FglAM to connect to FMS via HTTP.
Once the change has been done, restart the FMS and the FglAMs can be successfully added to FMS.