How to use the state variable from External material model in another Physics module?

Hi,

I developed a mechanical constitutive model by using the External material model. I want to use the state variable calculated from the External material model, say damage or plastic strain, in the Darcy's module. I input the variable "extmat1.state.Damage1" into Darcy's module, but the module cannot recgonise the variabe. Does anyone have encountered the same issue? How to solve it?

Thank you for your help and time.