Java Exception after attempting Gradle install and reverting to command line

[lmichlsen]

I had the java jar running fine at a command line.
I then attempted the Gradle / wrapper install. It installed fine but my organization will not let me access the 8080 or 8082 port.

So I attempted to run the command line again and I now get error
"Exception in thread "main" java.lang.UnsupportedClassVersionError: ServerKt has been compiled by a more recent version of the Java Runtime (class file version 55.0), this version of the Java Runtime only recognizes class file versions up to 52.0"

How can I revert to the command line version?