Custom Spawning Condition can't be put in.

The issue is that I spent a long time creating a spawning condition for an entity (You have to place Netherite blocks in a certain manner with a player head on top) and had it checked for errors and everything, it is currently part of my mod elements, yet whenever I try pulling up the dropdown menu for Custom Spawning Condition, the only option to pick from is (use vanilla condition) I spent a long time making sure all of the netherite blocks are supposed to be placed correctly and really want this to work so any help would be much appreciated!