update api register

app/Models/UserNotification.php

@@ -13,5 +13,13 @@ class UserNotification extends Model
         return ['read_at' => 'datetime'];
     }
 
-    public function user() { return $this->belongsTo(User::class); }
+    public function user()
+    {
+        return $this->belongsTo(User::class);
+    }
+
+    public function campaign()
+    {
+        return $this->belongsTo(SystemNotificationCampaign::class, 'system_notification_campaign_id');
+    }
 }