Using Spotify Android SDK in Unity

package com.unity3d.player;

import android.os.Bundle;
import com.unity3d.player.UnityPlayerActivity;
import android.content.Intent;
import android.content.IntentFilter;

import android.util.Log;

import com.spotify.android.appremote.api.ConnectionParams;
import com.spotify.android.appremote.api.Connector;
import com.spotify.android.appremote.api.SpotifyAppRemote;

import com.spotify.protocol.client.Subscription;
import com.spotify.protocol.types.PlayerState;
import com.spotify.protocol.types.Track;

public class MainActivity extends UnityPlayerActivity 
{
    public static MainActivity instance; // For Unity C# to trigger functions here
    public static String currentPlaying = ""; // For Unity C# to read current playing info
    
    private static final String CLIENT_ID = "your client id"; // Use your own Client Id
    private static final String REDIRECT_URI = "http://localhost:5000/callback"; // Also match this on the app settings page
    private SpotifyAppRemote mSpotifyAppRemote;

    @Override
    protected void onCreate(Bundle savedInstanceState) 
    {
        super.onCreate(savedInstanceState);
        instance = this;
    }
    
    // Triggered by Unity C# script
    public void PlaySong(String trackId) 
    {
        mSpotifyAppRemote.getPlayerApi().play("spotify:track:" + trackId);
    }

    @Override
    protected void onStart() 
    {
        super.onStart();
        ConnectionParams connectionParams =
                new ConnectionParams.Builder(CLIENT_ID)
                        .setRedirectUri(REDIRECT_URI)
                        .showAuthView(true)
                        .build();

        SpotifyAppRemote.connect(this, connectionParams, new Connector.ConnectionListener() 
        {
            public void onConnected(SpotifyAppRemote spotifyAppRemote) 
            {
                mSpotifyAppRemote = spotifyAppRemote;
                Log.d("MainActivity", "Connected! Yay!");

                // Now you can start interacting with App Remote
                connected();

            }

            public void onFailure(Throwable throwable) {
                Log.e("MyActivity", throwable.getMessage(), throwable);

                // Something went wrong when attempting to connect! Handle errors here
            }
        });
    }

    @Override
    protected void onStop() 
    {
        super.onStop();
        SpotifyAppRemote.disconnect(mSpotifyAppRemote);
    }

    private void connected() 
    {
        // Play a playlist
        mSpotifyAppRemote.getPlayerApi().play("spotify:playlist:37i9dQZF1DX2sUQwD7tbmL");

        // Subscribe to PlayerState
        mSpotifyAppRemote.getPlayerApi()
                .subscribeToPlayerState()
                .setEventCallback(playerState -> 
                {
                    final Track track = playerState.track;
                    if (track != null) {
                        Log.d("MainActivity", track.name + " by " + track.artist.name);
                        currentPlaying = track.name + " by " + track.artist.name;
                    }
                });
    }
}

using System;
using UnityEngine;
using UnityEngine.UI;

public class ExampleScript : MonoBehaviour
{
    private AndroidJavaClass mainActivityClass;
    private AndroidJavaObject mainActivityObject;
    
    public Text currentPlayingText;

    void Start()
    {
        mainActivityClass = new AndroidJavaClass("com.unity3d.player.MainActivity");
        mainActivityObject = mainActivityClass.GetStatic<AndroidJavaObject>("instance");
    }
    
    private void Update()
    {
        UpdateCurrentPlaying();
    }

    public void PlaySong()
    {
        mainActivityObject.Call("PlaySong","4SFknyjLcyTLJFPKD2m96o"); // BLACKPINK - How You Like That
    }

    public void UpdateCurrentPlaying()
    {
        currentPlayingText.text = mainActivityClass.GetStatic<string>("currentPlaying");
    }
}

package com.unity3d.player;
import android.content.BroadcastReceiver;
import android.content.Context;
import android.content.Intent;
import android.util.Log;

public class MyBroadcastReceiver extends BroadcastReceiver 
{
    static final class BroadcastTypes 
    {
        static final String SPOTIFY_PACKAGE = "com.spotify.music";
        static final String PLAYBACK_STATE_CHANGED = SPOTIFY_PACKAGE + ".playbackstatechanged";
        static final String QUEUE_CHANGED = SPOTIFY_PACKAGE + ".queuechanged";
        static final String METADATA_CHANGED = SPOTIFY_PACKAGE + ".metadatachanged";
    }
    
    public static String currentPlaying = ""; // For Unity C# to read current playing info
    
    @Override
    public void onReceive(Context context, Intent intent) 
    {
        long timeSentInMs = intent.getLongExtra("timeSent", 0L);

        String action = intent.getAction();

        if (action.equals(BroadcastTypes.METADATA_CHANGED)) 
        {
            String trackId = intent.getStringExtra("id");
            String artistName = intent.getStringExtra("artist");
            String albumName = intent.getStringExtra("album");
            String trackName = intent.getStringExtra("track");
            int trackLengthInSec = intent.getIntExtra("length", 0);
            // Do something with extracted information...
            currentPlaying = trackName + " by " + artistName;
        } 
        else if (action.equals(BroadcastTypes.PLAYBACK_STATE_CHANGED)) 
        {
            boolean playing = intent.getBooleanExtra("playing", false);
            int positionInMs = intent.getIntExtra("playbackPosition", 0);
            // Do something with extracted information
        } 
        else if (action.equals(BroadcastTypes.QUEUE_CHANGED)) 
        {
            // Sent only as a notification, your app may want to respond accordingly.
        }
    }
}

        <activity android:name=".MainActivity"
                ...bla bla bla...
        </activity>
        <receiver
                android:name=".MyBroadcastReceiver"
                android:enabled="true"
                android:exported="true">
            <intent-filter>
                <action android:name="com.spotify.music.playbackstatechanged"/>
                <action android:name="com.spotify.music.metadatachanged"/>
                <action android:name="com.spotify.music.queuechanged"/>
            </intent-filter>
        </receiver>

    @Override
    protected void onCreate(Bundle savedInstanceState) 
    {
        super.onCreate(savedInstanceState);
        instance = this;
        
        var receiver = new MyBroadcastReceiver();
        var filter1 = new IntentFilter("com.spotify.music.playbackstatechanged");
        var filter2 = new IntentFilter("com.spotify.music.metadatachanged");
        var filter3 = new IntentFilter("com.spotify.music.queuechanged");
        registerReceiver(receiver, filter1);
        registerReceiver(receiver, filter2);
        registerReceiver(receiver, filter3);
        Log.d("MainActivity", "Receiver Registered!");
    }