How to solve parse error while installing android app? - xamarin.android

Question

I'm creating an app using Xamarin.Forms .
This app runs correctly on emulator (android version 7.1) in Visual Studio 2017.
But gives "Parse Error : There was problem parsing the package." while installing it on my phone (Android version : 5.1).
Can anyone please help in solving this issue ????
Thanks in advance !!!!
ToastService Class
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using Android.App;
using Android.Content;
using Android.OS;
using Android.Runtime;
using Android.Views;
using Android.Widget;
namespace XamService.Droid.Services
{
[Service(Exported = true , Name = "XamService.ToastService")]
class ToastService : Service
{
public override IBinder OnBind(Intent intent)
{
throw new NotImplementedException();
}
[return: GeneratedEnum]
public override StartCommandResult OnStartCommand(Intent intent, [GeneratedEnum] StartCommandFlags flags, int startId)
{
Toast.MakeText(Android.App.Application.Context, "This is a toast from service !", ToastLength.Long).Show();
return StartCommandResult.Sticky;
}
}
}
ServiceCaller class
using Android.App;
using Android.Content;
using XamService.Interfaces;
using XamService.Droid.Services;
using XamService.Droid;
using Xamarin.Forms;
[assembly:Dependency(typeof(ServiceCaller))]
namespace XamService.Droid
{
class ServiceCaller : Activity, ICaller
{
public void serviceCaller()
{
Intent intent = new Intent(Forms.Context, typeof(ToastService));
Forms.Context.StartService(intent);
}
}
}
AndoridManifest
<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
android:versionCode="1"
android:versionName="1.0"
package="com.companyname.XamService"
android:installLocation="auto">
<uses-sdk android:minSdkVersion="15" />
<application android:label="XamService.Android">
<service android:name="ToastService" enabled="true"></service>
</application>
</manifest>