How to access REST API for P6 EPPM on premise

Hello I am trying to access the P6 REST API using Java Traditional method

P6 it is installed on premise:

The code is from Oracle Sample Guide.

Is it REST API available for on premise?

Is any configuration that should be done before this?

The error message that I recive:

"Exception in thread "main" java.io.IOException: Server returned HTTP response code: 401 for URL: http://localhost:8206/p6ws/restapi/user?user_0&Fields=Name

at sun.net.www.protocol.http.HttpURLConnection.getInputStream0(HttpURLConnection.java:1876)

at sun.net.www.protocol.http.HttpURLConnection.getInputStream(HttpURLConnection.java:1474)

at sampleprogram.SampleProgram.callRestURL(SampleProgram.java:55)

at sampleprogram.SampleProgram.main(SampleProgram.java:35)