Necropolis crafting, what am I doing wrong ???

Not sure, what I am doing wrong but no matter what corpses I bury, I can't craft, it tells me, there has to be another of the same kind. so, I buried all beast in one row, all undead etc. in one row. What am I doing wrong, I watched several videos, still don't get it and no, my IQ is not low?
Any advice ? Please

Somewhere in your graveyard there is a corpse buried with the line "Requires at least x other Corpse of the same Monster Name". Remove this corpse by clicking the shovel in the lower right corner.