IL Spot should be available for Injured Roster Players, not for Stashing Inj.
If you add an injured player from free agent, the player shouldn't be placed on IL list for at least two weeks, because the purpose of IL spot is for Injured players in the Roster.
Benn Wheeler commented
Agree with comment made on 23 November - there are no issues with this at all since you have to drop an active player to "stash" a player that is already injured
You have to add the IL player to your active roster first, and then move the player to the IL. The manager making this move is creating a slot in their active roster to add the IL player, so they are paying for the privilege, since IL players cannot be added directly to the IL slot.