Go to the BP_PlayerBuildingComponent and create a new variable called Grid Trace Channel and set its variable type to E_TraceTypeQuery. Set the default value to Gird
Add the highlighted nodes shown in the image below, location at the top of the image.










Go to the BuildPreview and create a new variable called Grid Trace Channel and set its variable type to E_TraceTypeQuery. Set the default value to Gird





