V20 Grandsteam transfer to BLF stopped working

[ronenba]

after upgrading to V20 the default of transfer to BLF is Attended transfer, and calls are disconnected

I downloaded XML of the phone showing the default is Attended

The workarounds I found are:
1. provision the Grandstream with the PBX
2. under maintenance - disable provisioning with 3CX
3. remove the address for the config
4. under Grandstream verify NAT is on STUN
5. under settings- call feature - Attended Transfer Mode - change it to Static "Blind Transfer"

then you can transfer calls to BLF

or if there is a way to modify phone XML change <!-- Attended Transfer Mode. 0 - Static, 1 - Dynamic. Default is 0 -->

Dynamic. Default is 1

and the upload it ( could not find how for now)