interface within interface

Try using this code, I believe this will suites your use case with showWhen property, 

PS: you can use if else for the same scenario, just stack the sectionLayouts (Interface1, Interface2) and check or any one condition for pressed button.

a!localVariables(
  /*pressed button variable, default value have to be there for showing 1st interface*/
  local!pressedButton: "cancel",
  a!sectionLayout(
    contents: {
      /*Interface 1*/
      a!sectionLayout(
        contents: {
          a!boxLayout(
            label: "Some form",
            contents: {
              a!textField(label: "Comments", readOnly: true),
              a!textField(label: "Start Date", readOnly: true),
              a!textField(label: "End Date", readOnly: true),
              a!textField(label: "Emial", readOnly: true),
              
            }
          ),
          a!buttonLayout(
            primaryButtons: {
              a!buttonWidget(label: "approve"),
              a!buttonWidget(
                label: "reject",
                value: "reject",
                saveInto: local!pressedButton
              )
            },
            secondaryButtons: { a!buttonWidget(label: "cancel") }
          )
        },
        showWhen: local!pressedButton = "cancel"
      ),
      /*Interface 2*/
      a!sectionLayout(
        contents: {
          a!boxLayout(
            label: "Some form",
            contents: {
              a!paragraphField(label: "Comments", readOnly: true)
            }
          ),
          a!buttonLayout(
            primaryButtons: {
              a!buttonWidget(
                label: "cancel",
                value: "cancel",
                saveInto: local!pressedButton
              ),
              a!buttonWidget(label: "submit")
            }
          )
        },
        showWhen: local!pressedButton = "reject"
      )
    }
  )
)

Thank you ,It worked

Thank you ,It worked