Error: fastboot:flash: Error: flashing failed: Error: {"error":{"killed":fa [...] FAILED (remote: 'not supported in locked device')\nfastboot: error: Command failed"}

[niweiwang]

UBports Installer 0.5.6-beta (dmg)
Environment: Mac OS X 10.13.6 macOS High Sierra darwin 17.7.0 x64 17G14033 with Node.js v12.16.3
Device: hammerhead
Target OS: Ubuntu Touch
Settings: undefined
OPEN-CUTS run: https://ubports.open-cuts.org/run/5f9c09da9702a600079da037
Log: https://paste.ubuntu.com//p/W5cgyrSHtd/

Error:

Error: fastboot:flash: Error: flashing failed: Error: {"error":{"killed":false,"code":1,"signal":null,"cmd":"\"/Applications/ubports-installer.app/Contents/Resources/app.asar.unpacked/node_modules/android-tools-bin/dist/darwin/x86/fastboot\" flash boot '/Users/yiwei/Library/Caches/ubports/hammerhead/firmware/boot-hammerhead.img'"},"stdout":"","stderr":"Sending 'boot' (12302 KB)                          OKAY [  0.578s]\nWriting 'boot'                                     FAILED (remote: 'not supported in locked device')\nfastboot: error: Command failed"}

[NeoTheThird]

Duplicate of #1468. Should be fixed in this pre-release version.