If I place blueprint with variables, I do not get your variables GUI.
I am playing with a bunch of mods, so, could them conflicts?

I have heard that only one blueprint handler can be assigned at a time (i.e. one mod)
If this is the case, I would suggest a workaround:
Create an additional new tool, and after selecting entities open your GUI to replace variables.

ah, got the issue.
Player must copy a blueprint to its inventory from the blueprint library before placement.
Works ONLY for blueprints in the inventory.

Please add it to the mod description.

Hey saaadel, it shouldn't work that way. I will look into this.

It should activate on ghost placement (entity creation) while holding a blueprint or blueprint book.

I use the following scenario here:
- open the player's blueprints library
- select a book, open it with a right click
- select a blueprint, take it in hands
- close the blueprints library, and place the blueprint on the surface
- no variable mapping popup for me here :(

But if I place the blueprint into the inventory before (or duplicate it) — it works

Should be working now!