"Add turret & ammo box" - How to activate?

Hi.

I'm kind of "done" with Akua.

I want to build a CV next, but I'd like to move past the "base building" goals.

Unfortunately, I cannot move past the "add turret & ammo box" goal.
I have added small and big ammo boxes to my home-base, added some flak turret, more ammo boxes and another flak turret and still it's not "checked". Added ammo in the boxes too. All did nothing.

Does it need a specific turret type? Or many turrets or what?