Fill the space with foliage limited by volume

How to randomly fill a volume (custom mesh) with foliage (or other meshes)? I’ve tried using procedural foliage volume, but whatever I do, it keeps saying “Unable to spawn instances. Ensure a large enough surface exists within a volume”. Perhaps this is because it is still an experimental feature. Is there a way to write a simple blueprint that fills the space with foliage (or meshes) limited by volume (custom mesh)?