ember multi level has many serialization issue

I am facing some issues with my serialization of model. Below is a detailed code which will show how my current model and corresponding serializers look.

1. User model

   export default Model.extend({
     name: attr('string'),
     accounts: hasMany('account', {async: false})
   });
   
   

2. Account model

    export default Model.extend({
        type: attr('string'),
        transactions: hasMany('transaction')
    })
   
   

3. Transaction model

    export default Model.extend({
       date: attr('string'),
       amount: attr('number')
    })
   
   

So basically its a hasMany within another hasMany.

Serializers looks like this:

1. base serializer:

    export default BaseSerializer.extend({
       keyForAttribute(key) {
         return key.underscore();
       },
       keyForRelationship(key, relationship) {
          return key.underscore();
       }
      });
   
   

2. User serializer:

   export default BaseSerializer.extend(DS.EmbeddedRecordsMixin, {
    attrs: {
      account: { embedded: 'always' }
    }
   });
   
   

3. Account serializer:

   export default BaseSerializer.extend(DS.EmbeddedRecordsMixin, {
    attrs: {
      transaction: { embedded: 'always' }
    }
   });
   
   

Now when I am invoking api call which gives me a json response where user model has a property named as accounts: which internally have another property called as transactions, I am expecting them to serialize but somehow its not working. have I done anything wrong here? Please advise as I am new to ember and still learning it.