Techtree Requirement for Sold Unit

[CivSavage]

I have a unit that sells another unit (it's like an upgrade to a new unit, the original unit is removed by trigger after its sold). The problem is I want selling the unit to require a technology or upgrade before it's able to be sold. Putting this upgrade in 'Techtree - Requirements' in the Object Editor field for the new unit doesn't work however, you are still able to buy it.

What is the easiest way around this? Keep in mind that I have many units that do this and many techtree requirements for each unit.

 

[EvilPotato]

How does the unit sell? By selecting other unit with an ability?
You want the ability to be gray inside unit until its player gets technology?
Try to set these 2 fields inside the ability:
1) Techtree requirments = the needed tecmology
2) Techtree - check dependencies = true

 

[CivSavage]

Got it working, thanks.