FLStudio's plugin manager is not up to date with the latest versions of the SDK.
This was taken from the page "VST 3 Locations / Format" in the SDK documentation:
[quote]
On the Windows platform a VST 3 Plug ...
every plugin and troubleshot all I can think of but to no luck.
I am using the latest build of FL 12.5.1 (build 5)
If anyone can offer up any advice I'd be happy to hear it.
Cheers,
Michael ...