If you have following error:
Using device: JAF FLASHER INTERFACE
 Interface: POTATO BOX
 » BOX FW Version: 01.B2
 » BOX Authentication ...failed!
 Error opening !
 Last error: The handle is invalid (code: 6)
 JAF FLASHER INTERFACE disconnected.

That means you are using latest MxKey v3.3 revision 1.7 with an JAF box with PATCHED firmware 01.B2 written inside (used Potato Firmware Updater v2.0).
Latest release of MxKey solved JAF Box crypted Authentification used by Potato & Co. to "protect" their boxes to no more be able to be used with 3rd party softwares. Now MxKey v3.3 revision 1.7 support well Authentification with original JAF Box firmwares 01.B2 and 01.B4.

So, to solve the error described here :The handle is invalid (code: 6)
just download POTATO JAF Box Firmware Updater v4.0 from here:

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and write any ORIGINAL firmware inside your JAF Box.
To be able to use latest release with New Flash Protocol, is required to write Original Firmware 01.B4