How to show error at autocompleteTextView dropdown if user doesn't select in android?

Question

I have question to answer my curiosity. I have implemented dropdown with material design like snippet code xml at the below

   <com.google.android.material.textfield.TextInputLayout
        android:id="@+id/provinsi_register_form"
        style="@style/Widget.MaterialComponents.TextInputLayout.OutlinedBox.ExposedDropdownMenu"
        android:layout_width="0dp"
        android:layout_height="wrap_content"
        android:layout_marginStart="24dp"
        android:layout_marginTop="16dp"
        android:layout_marginEnd="24dp"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toBottomOf="@+id/address_register_form">

        <AutoCompleteTextView
            android:id="@+id/filled_dropdown_provinsi"
            style="@style/greySubText"
            android:layout_width="match_parent"
            android:layout_height="55dp"
            android:hint="@string/provinsi_form"
            android:inputType="none" />
    </com.google.android.material.textfield.TextInputLayout>

You can see the result implementation on this link picture result dropdown

for the list, I got from ViewModel like on this snipet code below:

 konfirmasiViewModel.provinsi.observe(this, { provinsi ->
        for (i in provinsi.indices) {
            provinsiNama.add(provinsi[i].provinsi!!)
        }
        val adapter =
            ArrayAdapter(this, R.layout.support_simple_spinner_dropdown_item, provinsiNama)
        filled_dropdown_provinsi.setAdapter(adapter)
        filled_dropdown_provinsi.setOnItemClickListener { adapterView, view, i, l ->
            lifecycleScope.launch {
                siscaPreference.saveId(provinsi[i].id!!)
            }
            prov = provinsi[i].id.toString()
        }
    })

How to make condition if user doesn't choose anything either click by button or not? Thanks for much attention