when i try to download sdk through moonshine or sdk nstaller, it fails with error below.
Thank you, for reporting this! Alternatively, you can report issues to Moonshine Git as well (here).
Unfortunately, there were some limitation to the older SDK installer source (and integrated to Moonshine) - where the installer failing downloading latest Adobe AIR SDK. This is a known issue and already discussed at https://github.com/prominic/Moonshine-IDE/issues/119.
Moonshine had the SDK installer source updated (with Apache) and waiting for a release.
Until then, you can download SDKs through official Apache Flex SDK Installer (here), and *maybe* - you also need to follow the following steps /if/ encounter any SDK downloading problem (mentioned in Moonshine issue page) :
If you encounter errors downloading SDKs through Moonshine (or Moonshine App Store Helper for macOS), you may be able to resolve them by installing JCE in your Java installation: