[SOLVED] nexus: Could not transfer artifact from/to nexus (http://localhost:8081/repository/maven-proxy-test/)

I installed nexus repository manager 3 in my system. I configured maven2 proxy repository, when i tried to clean pom.xml file using 'mvn clean' command, I am getting below error.

[INFO] Scanning for projects...
[INFO] 
[INFO] ------------------< com.sample.app:nexus-proxy-test >-------------------
[INFO] Building nexus-proxy-test 1.0-SNAPSHOT
[INFO] --------------------------------[ jar ]---------------------------------
Downloading from nexus: http://localhost:8081/repository/maven-proxy-test/org/apache/maven/plugins/maven-clean-plugin/2.5/maven-clean-plugin-2.5.pom
[INFO] ------------------------------------------------------------------------
[INFO] BUILD FAILURE
[INFO] ------------------------------------------------------------------------
[INFO] Total time:  0.377 s
[INFO] Finished at: 2019-10-03T19:04:32+05:30
[INFO] ------------------------------------------------------------------------
[ERROR] Plugin org.apache.maven.plugins:maven-clean-plugin:2.5 or one of its dependencies could not be resolved: Failed to read artifact descriptor for org.apache.maven.plugins:maven-clean-plugin:jar:2.5: Could not transfer artifact org.apache.maven.plugins:maven-clean-plugin:pom:2.5 from/to nexus (http://localhost:8081/repository/maven-proxy-test/): Not authorized -> [Help 1]
[ERROR] 
[ERROR] To see the full stack trace of the errors, re-run Maven with the -e switch.
[ERROR] Re-run Maven using the -X switch to enable full debug logging.
[ERROR] 
[ERROR] For more information about the errors and possible solutions, please read the following articles:
[ERROR] [Help 1] http://cwiki.apache.org/confluence/display/MAVEN/PluginResolutionException

Error stack trace looks like below.

Caused by: org.apache.maven.wagon.authorization.AuthorizationException: Not authorized
    at org.apache.maven.wagon.providers.http.wagon.shared.AbstractHttpClientWagon.resourceExists (AbstractHttpClientWagon.java:838)
    at org.apache.maven.wagon.providers.http.wagon.shared.AbstractHttpClientWagon.resourceExists (AbstractHttpClientWagon.java:809)
    at org.eclipse.aether.transport.wagon.WagonTransporter$PeekTaskRunner.run (WagonTransporter.java:512)
    at org.eclipse.aether.transport.wagon.WagonTransporter.execute (WagonTransporter.java:435)
    at org.eclipse.aether.transport.wagon.WagonTransporter.peek (WagonTransporter.java:406)
    at org.eclipse.aether.connector.basic.BasicRepositoryConnector$PeekTaskRunner.runTask (BasicRepositoryConnector.java:390)
    at org.eclipse.aether.connector.basic.BasicRepositoryConnector$TaskRunner.run (BasicRepositoryConnector.java:364)
    at org.eclipse.aether.util.concurrency.RunnableErrorForwarder$1.run (RunnableErrorForwarder.java:75)
    at org.eclipse.aether.connector.basic.BasicRepositoryConnector$DirectExecutor.execute (BasicRepositoryConnector.java:644)
    at org.eclipse.aether.connector.basic.BasicRepositoryConnector.get (BasicRepositoryConnector.java:262)
    at org.eclipse.aether.internal.impl.DefaultArtifactResolver.performDownloads (DefaultArtifactResolver.java:499)
    at org.eclipse.aether.internal.impl.DefaultArtifactResolver.resolve (DefaultArtifactResolver.java:401)
    at org.eclipse.aether.internal.impl.DefaultArtifactResolver.resolveArtifacts (DefaultArtifactResolver.java:229)
    at org.eclipse.aether.internal.impl.DefaultArtifactResolver.resolveArtifact (DefaultArtifactResolver.java:207)
    at org.apache.maven.repository.internal.DefaultArtifactDescriptorReader.loadPom (DefaultArtifactDescriptorReader.java:240)
    at org.apache.maven.repository.internal.DefaultArtifactDescriptorReader.readArtifactDescriptor (DefaultArtifactDescriptorReader.java:171)
    at org.eclipse.aether.internal.impl.DefaultRepositorySystem.readArtifactDescriptor (DefaultRepositorySystem.java:255)
    at org.apache.maven.plugin.internal.DefaultPluginDependenciesResolver.resolve (DefaultPluginDependenciesResolver.java:106)
    at org.apache.maven.plugin.internal.DefaultMavenPluginManager.getPluginDescriptor (DefaultMavenPluginManager.java:182)
    at org.apache.maven.plugin.internal.DefaultMavenPluginManager.getMojoDescriptor (DefaultMavenPluginManager.java:286)
    at org.apache.maven.plugin.DefaultBuildPluginManager.getMojoDescriptor (DefaultBuildPluginManager.java:244)
    at org.apache.maven.lifecycle.internal.DefaultLifecycleExecutionPlanCalculator.setupMojoExecution (DefaultLifecycleExecutionPlanCalculator.java:169)
    at org.apache.maven.lifecycle.internal.DefaultLifecycleExecutionPlanCalculator.setupMojoExecutions (DefaultLifecycleExecutionPlanCalculator.java:154)
    at org.apache.maven.lifecycle.internal.DefaultLifecycleExecutionPlanCalculator.calculateExecutionPlan (DefaultLifecycleExecutionPlanCalculator.java:130)
    at org.apache.maven.lifecycle.internal.DefaultLifecycleExecutionPlanCalculator.calculateExecutionPlan (DefaultLifecycleExecutionPlanCalculator.java:144)
    at org.apache.maven.lifecycle.internal.builder.BuilderCommon.resolveBuildPlan (BuilderCommon.java:97)
    at org.apache.maven.lifecycle.internal.LifecycleModuleBuilder.buildProject (LifecycleModuleBuilder.java:111)
    at org.apache.maven.lifecycle.internal.LifecycleModuleBuilder.buildProject (LifecycleModuleBuilder.java:81)
    at org.apache.maven.lifecycle.internal.builder.singlethreaded.SingleThreadedBuilder.build (SingleThreadedBuilder.java:56)
    at org.apache.maven.lifecycle.internal.LifecycleStarter.execute (LifecycleStarter.java:128)
    at org.apache.maven.DefaultMaven.doExecute (DefaultMaven.java:305)
    at org.apache.maven.DefaultMaven.doExecute (DefaultMaven.java:192)
    at org.apache.maven.DefaultMaven.execute (DefaultMaven.java:105)
    at org.apache.maven.cli.MavenCli.execute (MavenCli.java:956)
    at org.apache.maven.cli.MavenCli.doMain (MavenCli.java:288)
    at org.apache.maven.cli.MavenCli.main (MavenCli.java:192)
    at sun.reflect.NativeMethodAccessorImpl.invoke0 (Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke (NativeMethodAccessorImpl.java:62)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke (DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke (Method.java:498)
    at org.codehaus.plexus.classworlds.launcher.Launcher.launchEnhanced (Launcher.java:282)
    at org.codehaus.plexus.classworlds.launcher.Launcher.launch (Launcher.java:225)
    at org.codehaus.plexus.classworlds.launcher.Launcher.mainWithExitCode (Launcher.java:406)
    at org.codehaus.plexus.classworlds.launcher.Launcher.main (Launcher.java:347)

Reference https://help.sonatype.com/learning/repository-manager-3/first-time-installation-and-setup/lesson-2%3A-proxy-and-hosted-maven-repositories