FOnMountPak IsBound always returns false

I’m trying since some days to mount a pak file in order to open its levels and use its assets. I’ve read a lot of threads on this argument (I think all of them) and still can’t find a valid solution.
I’ve ended with using FPakPlatformFile and FPakFile to mount a pak and then I tried to load an inner level, but I just obtained a lot of errors.

I would like to use the following code to mount a pak file:

FCoreDelegates::OnMountPak.Execute(PakLocation, 0);

but can’t use it because FCoreDelegates::OnMountPak.IsBound() always returns false. I’ve tried with PIE mode, with standalone and also with a packaged version. Always it returns false.
May someone suggest me how to use this way to mount a pak?