I’m trying this under UE 5.1 and it doesn’t appear to work. Added a WaterBodyCustom, kept the default Water_Material_CustomMesh material, set Water Mesh Override to Cube, set the spline Z to 50 which was the top of the cube and ticked Auto-Activate. Added a BP_FluidSim_01 and a BP_Bouyancy_Example and simulated. The cube just dropped to the bottom like a stone.
I can get this to work with Water Body Lake or Water Body Ocean, but not Water Body Custom. Is there even any documentation out there on this plugin that I can follow to ensure I’m setting this up correctly?