Tried with stock recovery:
Code:
> .\adb.exe sideload ..\update.zip
serving: '..\update.zip' (~47%) adb: failed to read command: No error
Logs in boox recovery:
Code:
Supported API: 3
Finding update package...
Verifying update package
E:failed to verify whole-file signature
Update package verification took 79.3 s (result 1).
E:Signature verification failed
E:error: 21
Install from ADB completed with status 2.
Installation aborted.