Unityで実行時にUnable to resolve superclassエラー

みていただきありがとうございます

unityにて自作したプラグインを実行した際に以下のようなエラーが発生しました。

W/dalvikvm(11322): Unable to resolve superclass of Lcom/google/firebase/messaging/FirebaseMessagingService; (4817)
W/dalvikvm(11322): Link of class 'Lcom/google/firebase/messaging/FirebaseMessagingService;' failed
W/dalvikvm(11322): Unable to resolve superclass of Lcom/myplugin/fcm/CustomMessagingService; (4825)
W/dalvikvm(11322): Link of class 'Lcom/myplugin/fcm/CustomMessagingService;' failed
E/dalvikvm(11322): Could not find class 'com.myplugin.fcm.CustomMessagingService', referenced from method com.myplugin.fcm.Provider.initialize
W/dalvikvm(11322): VFY: unable to resolve const-class 6000 (Lcom/myplugin/fcm/CustomMessagingService;) in Lcom/myplugin/fcm/Provider;
W/ComponentDiscovery(11322): Application info not found.
W/ComponentDiscovery(11322): Could not retrieve metadata, returning empty list of registrars.
W/dalvikvm(11322): VFY: unable to resolve virtual method 584: Landroid/content/Context;.createDeviceProtectedStorageContext ()Landroid/content/Context;
W/dalvikvm(11322): VFY: unable to resolve virtual method 592: Landroid/content/Context;.getCodeCacheDir ()Ljava/io/File;
W/dalvikvm(11322): VFY: unable to resolve virtual method 593: Landroid/content/Context;.getColor (I)I
W/dalvikvm(11322): VFY: unable to resolve virtual method 594: Landroid/content/Context;.getColorStateList (I)Landroid/content/res/ColorStateList;
W/dalvikvm(11322): VFY: unable to resolve virtual method 596: Landroid/content/Context;.getDataDir ()Ljava/io/File;
W/dalvikvm(11322): VFY: unable to resolve virtual method 597: Landroid/content/Context;.getDrawable (I)Landroid/graphics/drawable/Drawable;
W/dalvikvm(11322): VFY: unable to resolve virtual method 604: Landroid/content/Context;.getNoBackupFilesDir ()Ljava/io/File;
W/dalvikvm(11322): VFY: unable to resolve virtual method 617: Landroid/content/Context;.isDeviceProtectedStorage ()Z
W/dalvikvm(11322): VFY: unable to resolve virtual method 634: Landroid/content/Context;.startForegroundService (Landroid/content/Intent;)Landroid/content/ComponentName;
E/Unity   (11322): AndroidJavaException: java.lang.NoClassDefFoundError: com.myplugin.fcm.CustomMessagingService
E/Unity   (11322): java.lang.NoClassDefFoundError: com.myplugin.fcm.CustomMessagingService
E/Unity   (11322):  at com.myplugin.fcm.Provider.initialize(Provider.java:18)
E/Unity   (11322):  at com.unity3d.player.UnityPlayer.nativeRender(Native Method)
E/Unity   (11322):  at com.unity3d.player.UnityPlayer.c(Unknown Source)
E/Unity   (11322):  at com.unity3d.player.UnityPlayer$c$1.handleMessage(Unknown Source)
E/Unity   (11322):  at android.os.Handler.dispatchMessage(Handler.java:98)
E/Unity   (11322):  at android.os.Looper.loop(Looper.java:136)
E/Unity   (11322):  at com.unity3d.player.UnityPlayer$c.run(Unknown Source)
E/Unity   (11322):   at UnityEngine.AndroidJNISafe.CheckException () [0x0008c] in /Users/builduser/buildslave/unity/build/Runtime/Export/AndroidJNISafe.cs:24 
E/Unity   (11322):   at UnityEngine.AndroidJNISafe.CallStaticVoidMethod (IntPtr clazz, IntPtr methodID, UnityEngine.jvalue[] args) [0x00011] in /Users/builduser/buildslave/unity/build/Runtime/Export/AndroidJNISafe.cs:202 
E/Unity   (11322):   at UnityEngine.AndroidJavaObject._CallStatic (Sy

以下のようなクラスです

public class CustomMessagingService extends FirebaseMessagingService {
...
}

FirebaseMessagingServiceがapkに含まれていないのではないかと思い、AndroidStudioでAnalyzeしてみましたが、含まれているようでした。

原因に検討がつかず、質問させていただきます。
よろしくお願いします