How to update the custom Android ROM

1. Download the ROM zip file on a computer
2. Connect the phone to the computer, reboot to recovery, and install the ROM

adb devices
adb reboot recovery
adb sideload ROM.zip

Installer message serving: 'ROM.zip' (~47%) adb: failed to read command: Success means that everything is okay.

Reddit - adb: failed to read command: Success

That's an ADB issue, nothing is wrong with the device, cable, PC or the installation process. If I remember correctly (from a discussion long ago), Google's ROMs are transferred about 2.2 times across the sideload. To make the progress bar add up to 100%, they said "2.2 times the file size equals 100%". Our ZIPs are transferred just once, so the final progress is at about 47% with a success. The xfer seems to show the transferred data compared to the file size. Ours clocks in at x1.00 or x1.01, while Google's is about x2.something.

3. Reboot to the system
4. Install the Magisk app
5. Reboot to recovery again, and install Magisk zip

adb reboot recovery
adb sideload Magisk.zip

6. Reboot to the system
7. Check SafetyNet