Hello Amalia,
Try to include your read cube name in the Planning Filter and in the fox try to crate a local variable which should hold your Keyfigure you wanted in that cube and you can use this local variable.
EX:
ZLOCVAR = {"YPUR Keyfigure",x,x,x,x,x,"your read cube",x,x,x,x,}.
then you can use this local variable as
{zkf,x,x,x,x,target cube,x,x,x,x} = zlocvar.
Try like this and it may help you!!!
With Regards,
PJ