Trying to make a ToggleButton with images, getting error: <item> tag requires a 'drawable' attribute or child tag defining a drawable

I am trying to follow a simple tutorial online about making a toggle button in android with images (so it shows images instad of ON/OFF).

It doesn't work. The error I get is

-        Binary XML file line #1: <item> tag requires a 'drawable' attribute or child tag defining a drawable

I am using Visual Studio 2019 and coding with Xamarin.

I have a toggle button defined like this in my activity_main.xml:

  <ToggleButton
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_toLeftOf="@id/toggleButton1"
    android:background="@drawable/toggleButton_emp"
    android:id="@+id/toggleButtonEmp"/>

Then I have a "toggleButton_emp.xml" file in "Resources\drawable" which contains:

<?xml version="1.0" encoding="utf-8" ?>
<selector xmlns:android="http://schemas.android.com/apk/res/android">
  <item android:drawable="@drawable/faction4" android:state_checked="true"/>
  <item android:drawable="@drawable/faction3" android:state_checked="false" />
</selector>

faction4 and faction3 are valid drawables I have added to "Resources\drawable"

I have found many answers for this issue that are most 10 years old, and none help. They often say to make "drawable" first tag but it's already first. Or removing spaces but I don't have any.