[XA2 Plus] 3.0.2.8 flashing script does not work on Windows [answered]

Trying flashing 3.0.2.8 on my H4413. fastboot devices returns:

CQ3001AR38      fastboot

Double-clicking the shell, it closes after a while. Launching the script from an open shell returns the following:

Microsoft Windows [Versione 10.0.17134.648]
(c) 2018 Microsoft Corporation. Tutti i diritti sono riservati.
 
C:\Users\giacomo_2>cd C:\Users\giacomo_2\Desktop\Sailfish_OS-Jolla-3.0.2.8-h4413-0.0.7.12
 
C:\Users\giacomo_2\Desktop\Sailfish_OS-Jolla-3.0.2.8-h4413-0.0.7.12>flash-on-windows.bat
 
This is a Windows flashing script for Sony Xperia XA2 device.
 
Power on the device in fastboot mode, by doing the following:
1. Turn off your Xperia.
2. Connect one end of a USB cable to your PC.
3. While holding the volume up button pressed, connect the other end of
   the USB cable to your Xperia.
4. After this you should see the blue LED lit on Xperia, and it will be
   ready for flashing
 
Premere un tasto per continuare . . .
MD5SUM 'ed5a809dc0024d83cbab4fb9933d598d' match for file 'AdbWinApi.dll'.
MD5SUM '0e24119daf1909e398fa1850b6112077' match for file 'AdbWinUsbApi.dll'.
MD5SUM 'c980ea6caa9140ee3f30cdc0e98844c4' match for file 'fastboot.exe'.
MD5SUM 'e129a068a358f03f0857510151fc6d12' match for file 'flash-on-windows.bat'.
 
Searching a compatible device...
 
The device is unlocked for the flashing process. Continuing..
 
Impossibile trovare l'unità specificata.
 
Found 'SW_binaries_for_Xperia_Android_8.1.6.4_r1_v17_nile.img' that will be used as vendor image. Continuing..
or non atteso.
C:\Users\giacomo_2\Desktop\Sailfish_OS-Jolla-3.0.2.8-h4413-0.0.7.12>

"Impossibile trovare l'unità specificata" translates to "Can't find specified unit". "or not atteso" translates to "unexpected or".

I would like to get indications for debugging or possibly a manual procedure without risking to brick the device.

Tested both on Windows 7 and 10.