Running Android App with adb start (Error: Activity not started, unable to resolve Intent)

I am trying to run my own Android app from a Windows CMD using the adb shell. As per the official guide, I try to run adb shell am com.example.myapp.

The error I get is

Error: Activity not started, unable to resolve Intent {
act=android.intent.action.MAIN
cat=[android.intent.category.LAUNCHER]
flg=0x10000000
pkg=com.example.myapp }

When I run adb shell pm list packages | grep myapp I can see that the package is installed. Additionally, my AndroidManifest.xml does have the correct intent defined.

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
      package="com.example.myapp"
      android:versionCode="1"
      android:versionName="1.0">
    <application android:label="@string/app_name">
        <activity android:name=".DemoActivity"
                  android:label="@string/app_name">
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />
                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>
    </application>
</manifest>

Can anyone offer some advice on what is causing this error?