The current pre-release of the client ("pioneer" in the version) is only compatible to itself. So you can only play with other testers. Please be aware!
@LeFleurBang
from now on you can also start the FAF version directly wihtout using the FAF launcher.
Just make an desktop shortcut of the file C:\ProgramData\FAForever\bin\ForgedAlliance.exe
(ProgramData is a hidden folder!)