Invalid answer from server while trying to install

       Starting job of type [install] with identifier [extension/action/org.xwiki.contrib.confluence:confluence-syntax-xhtml]
        Starting job of type [installplan]
        Resolving extension [org.xwiki.contrib.confluence:confluence-syntax-xhtml/9.2.5] on all namespaces
        status code: 503, reason phrase: Service Temporarily Unavailable (503)
        Resolving extension dependency [XWiki Rendering - Syntax - XHTML 11.10.3] on all namespaces
        Resolving extension dependency [com.google.guava:guava-19.0] on all namespaces
        Resolving extension dependency [commons-io:commons-io-2.5] on all namespaces
        Finished job of type [installplan]
        Downloading extension [org.xwiki.contrib.confluence:confluence-syntax-xhtml/9.2.5]
        Invalid answer [500] from the server when requesting [http://extensions.xwiki.org/xwiki/rest/repository/extensions/org.xwiki.contrib.confluence%3Aconfluence-syntax-xhtml/versions/9.2.5/file]
        class org.xwiki.extension.repository.LocalExtensionRepositoryException: Failed to save extension [org.xwiki.contrib.confluence:confluence-syntax-xhtml/9.2.5] descriptor
            at org.xwiki.extension.repository.internal.local.DefaultLocalExtensionRepository.storeExtension(DefaultLocalExtensionRepository.java:187)
            at org.xwiki.extension.job.internal.InstallJob.storeExtension(InstallJob.java:186)
            at org.xwiki.extension.job.internal.InstallJob.store(InstallJob.java:171)
            at org.xwiki.extension.job.internal.InstallJob.runInternal(InstallJob.java:140)
            at org.xwiki.job.AbstractJob.runInContext(AbstractJob.java:240)
            at org.xwiki.job.AbstractJob.run(AbstractJob.java:217)
            at java.base/java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1128)
            at java.base/java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:628)
            at java.base/java.lang.Thread.run(Thread.java:834)
        Caused by: class java.io.IOException: Invalid answer [500] from the server when requesting [http://extensions.xwiki.org/xwiki/rest/repository/extensions/org.xwiki.contrib.confluence%3Aconfluence-syntax-xhtml/versions/9.2.5/file]
            at org.xwiki.extension.repository.xwiki.internal.XWikiExtensionRepository.getRESTResource(XWikiExtensionRepository.java:255)
            at org.xwiki.extension.repository.xwiki.internal.XWikiExtensionFile.openStream(XWikiExtensionFile.java:93)
            at org.xwiki.extension.repository.internal.local.DefaultLocalExtensionRepository.storeExtension(DefaultLocalExtensionRepository.java:178)
            at org.xwiki.extension.job.internal.InstallJob.storeExtension(InstallJob.java:186)
            at org.xwiki.extension.job.internal.InstallJob.store(InstallJob.java:171)
            at org.xwiki.extension.job.internal.InstallJob.runInternal(InstallJob.java:140)
            at org.xwiki.job.AbstractJob.runInContext(AbstractJob.java:240)
            at org.xwiki.job.AbstractJob.run(AbstractJob.java:217)
            at java.base/java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1128)
            at java.base/java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:628)
            at java.base/java.lang.Thread.run(Thread.java:834)
        Finished job of type [install] with identifier [extension/action/org.xwiki.contrib.confluence:confluence-syntax-xhtml]Confluence Syntax 1.1 9.2