The safest method is to use Apple’s hidden "App Store" redirect link. As of 2025, this link remains active:
and go to the official macOS High Sierra App Store page . Macos High Sierra 10.13.6 Raw Download
If you encounter the "installer payload failed" error during the process, it is often due to an outdated system date. You can fix this in Terminal by typing "date 0101010118" to reset the clock to a time when the High Sierra certificate was still valid. The safest method is to use Apple’s hidden