Ok, for me it works with Simbrief and the FBW A320
Steps to follow:
First of all, you should have this set in the tablet on the FWB A320, Options>Sim Options>set SYNC MSFS Flight Plan to NONE!
1. Simbrief flight plan
enter flight nr.
DEST & ARR airports
enter Aircraft Type A20N, not A320
enter passengers no., extra fuel, cargo
check if your flight plan is valid
generate flight plan
2. In MSFS go to World map and enter DEST. and ARR. airports, same as in Simbrief! Make it an IFR flight.
3. Start the airplane
Battery, then APU, then ADIRS to NAV
4. When screens are loaded, go to MCDU
Go to AOC menu
do INIT DATA REQUEST,
go to INIT PAGE, do REQUEST, your flight plan is loaded
5. Check GSX Menu
SIMBRIEF OK will be in green (otherwise you messed it up at Simbrief!)
6. Start Boarding, Catering, Fuel on the GSX Menu
That's it.
(if it still doesn't work, you should download the OFFLINE Addon Manager) Sticky subject in the Forum)