Mesh collider overlapping whole object

Trying to use a bridge from the asset store and put a mesh collider on, but this collider is overlapping the whole bridge, I can’t let my ball roll on it, it directly collides with the mesh, can someone help me with this?

which model it is (if its free one, then can test it) ?
Or have you accidentally enabled [×] convex mesh?

otherwise you might need to manually place primitive box colliders for each walls…

Oh no you were right!