That part of the process is the only part that is not our code running...it's P3D itself that seems to be stuck, because our installer simply starts P3D using the command line features that are used to configure an add-on to be enabled in the sim.
Have you already ran P3D at least once, and activated its license ? This might happen the first time you start it, for example if you install GSX right after installing or updating P3D without starting first at least once.