This one works better, thanks.
In short, a sheet body is a non-watertight geometry. It consists of faces only, and it’s completely hollow inside (i.e. it has no volume).
Repairing this kind of geometry can be very tricky (see this article). It consists of finding where the holes in the topology are, and closing them. The idea is not to have any free boundaries/naked edges that cause the geometry to be non-watertight.
Typically the best tool to fix the issue is the same one that constructed the geometry.
On a side note, I would really recommend using a smoother geometry for the simulation, the topology is quite detailed with hundreds of small faces:
This doesn’t mean that the CAD model is wrong, just that it’s not very good for a CFD simulation. I don’t think it’s possible to run a model this complex with a community account.
The other model that you linked (which is working) is definitely cleaner.
Cheers