Topology optimization

[skanskan]

Hello

I'm trying to perform a simple Topology optimization on a piece.
I want to minimize the volume of a piece while keeping the stress below a value.

I define the "design responses": strain_energy and volume, with the load case.
In the Objective I select the volume
But in the Constraint I cannot select the Strain from the list, it only shows "none".
If I try to create there a new design response I'm not able to "select object" for the "design response nodes"

How can I do it?

thanks.