Erro na comunicação com o Alexa Voice Service | Amazon Alexa: controle o seu ambiente com sua voz

Quando executo a comunicação com o Alexa Voice Service recebo os erro abaixo. Já tentei algumas coisas e não consegui resolver. Alguém sabe o que pode ser?

pi@orangepipc:~$ cd alexa-avs-sample-app/
pi@orangepipc:~/alexa-avs-sample-app$ cd samples
pi@orangepipc:~/alexa-avs-sample-app/samples$ cd javaclient && mvn exec:exec
[INFO] Scanning for projects...
Downloading: https://repo.maven.apache.org/maven2/org/apache/maven/plugins/maven-clean-plugin/2.5/maven-clean-plugin-2.5.pom
[WARNING] Failed to retrieve plugin descriptor for org.apache.maven.plugins:maven-clean-plugin:2.5: 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
Downloading: https://repo.maven.apache.org/maven2/org/apache/maven/plugins/maven-resources-plugin/2.6/maven-resources-plugin-2.6.pom
[WARNING] Failed to retrieve plugin descriptor for org.apache.maven.plugins:maven-resources-plugin:2.6: Plugin org.apache.maven.plugins:maven-resources-plugin:2.6 or one of its dependencies could not be resolved: Failed to read artifact descriptor for org.apache.maven.plugins:maven-resources-plugin:jar:2.6
Downloading: https://repo.maven.apache.org/maven2/org/apache/maven/plugins/maven-jar-plugin/2.4/maven-jar-plugin-2.4.pom
[WARNING] Failed to retrieve plugin descriptor for org.apache.maven.plugins:maven-jar-plugin:2.4: Plugin org.apache.maven.plugins:maven-jar-plugin:2.4 or one of its dependencies could not be resolved: Failed to read artifact descriptor for org.apache.maven.plugins:maven-jar-plugin:jar:2.4
Downloading: https://repo.maven.apache.org/maven2/org/apache/maven/plugins/maven-compiler-plugin/3.3/maven-compiler-plugin-3.3.pom
[WARNING] Failed to retrieve plugin descriptor for org.apache.maven.plugins:maven-compiler-plugin:3.3: Plugin org.apache.maven.plugins:maven-compiler-plugin:3.3 or one of its dependencies could not be resolved: Failed to read artifact descriptor for org.apache.maven.plugins:maven-compiler-plugin:jar:3.3
Downloading: https://repo.maven.apache.org/maven2/org/apache/maven/plugins/maven-surefire-plugin/2.17/maven-surefire-plugin-2.17.pom
[WARNING] Failed to retrieve plugin descriptor for org.apache.maven.plugins:maven-surefire-plugin:2.17: Plugin org.apache.maven.plugins:maven-surefire-plugin:2.17 or one of its dependencies could not be resolved: Failed to read artifact descriptor for org.apache.maven.plugins:maven-surefire-plugin:jar:2.17
Downloading: https://repo.maven.apache.org/maven2/org/apache/maven/plugins/maven-install-plugin/2.5.2/maven-install-plugin-2.5.2.pom
[WARNING] Failed to retrieve plugin descriptor for org.apache.maven.plugins:maven-install-plugin:2.5.2: Plugin org.apache.maven.plugins:maven-install-plugin:2.5.2 or one of its dependencies could not be resolved: Failed to read artifact descriptor for org.apache.maven.plugins:maven-install-plugin:jar:2.5.2
Downloading: https://repo.maven.apache.org/maven2/org/apache/maven/plugins/maven-deploy-plugin/2.7/maven-deploy-plugin-2.7.pom
...
[INFO] ------------------------------------------------------------------------
[INFO] BUILD FAILURE
[INFO] ------------------------------------------------------------------------
[INFO] Total time: 7.424 s
[INFO] Finished at: 2018-01-24T22:26:26-02:00
[INFO] Final Memory: 7M/17M

[INFO] ------------------------------------------------------------------------
[ERROR] No plugin found for prefix 'exec' in the current project and in the plugin groups [org.apache.maven.plugins, org.codehaus.mojo] available from the repositories [local (/home/pi/.m2/repository), central (https://repo.maven.apache.org/maven2)] -> [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/NoPluginFoundForPrefixException

Não postei está o erro completo pq o campo aqui não permite.

Consegui resolver essa parte, mas ainda tenho esse erro:

pi@orangepipc:~$ cd /home/pi/alexa-avs-sample-app/samples/javaclient && mvn exec:exec
[INFO] Scanning for projects...
[INFO]                                                                         
[INFO] ------------------------------------------------------------------------
[INFO] Building Alexa Voice Service Sample Java Client 20160207.7
[INFO] ------------------------------------------------------------------------
[INFO] 
[INFO] --- exec-maven-plugin:1.2.1:exec (default-cli) @ sample-java-client ---
Error: Could not find or load main class com.amazon.alexa.avs.App
[INFO] ------------------------------------------------------------------------
[INFO] BUILD FAILURE
[INFO] ------------------------------------------------------------------------
[INFO] Total time: 6.367 s
[INFO] Finished at: 2018-01-31T21:13:20-02:00
[INFO] Final Memory: 8M/19M
[INFO] ------------------------------------------------------------------------
[ERROR] Failed to execute goal org.codehaus.mojo:exec-maven-plugin:1.2.1:exec (default-cli) on project sample-java-client: Command execution failed. Process exited with an error: 1 (Exit value: 1) -> [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/MojoExecutionException
pi@orangepipc:~/alexa-avs-sample-app/samples/javaclient$