Go to the BP_BuildMaster and then go to the Starting Ignore Actor collapsed node. Create a new “Get all actors of class” node and set the class to “VoxelTerrainActor” or the class of your voxel actor. Then create a new then create a new array of “VoxelTerrainActors” and connect that to the get all actors of class output. Example image below.

Then find and right click the landscape actors array and find references.
Then just copy the same things the landscape actors variable is being used for and do the same for the “VoxelTerrainActor” that you created. Example image below.

Last if you go to the BuildPreview then go to the Hit Actor Check macro and add a pin to this Or node and connect up a new == node and set the class to “VoxelTerrainActor”, it should work. (Node you need to add the node highlighted node and set its class to Voxelterrainactor)