Embed nested collections form in Symfony 6 - forms

Question

I want to embed nested collections on three levels, for the second level it works but not the last one i can't get the prototype on the last level.
I work with Symfony 6 and i use stimulus.
class FormType1 extends AbstractType
{
public function buildForm(FormBuilderInterface $builder, array $options)
{
$builder
->add('field1')
->add('formType2', CollectionType::class, [
'entry_type' => FormType2::class,
'entry_options' => ['label' => false],
]);
}
public function configureOptions(OptionsResolver $resolver)
{
$resolver->setDefaults([
'data_class' => FormData1::class,
]);
}
}
class FormType2 extends AbstractType
{
public function buildForm(FormBuilderInterface $builder, array $options)
{
$builder
->add('field2')
->add('formType3', CollectionType::class, [
'entry_type' => FormType3::class,
'entry_options' => ['label' => false],
]);
}
public function configureOptions(OptionsResolver $resolver)
{
$resolver->setDefaults([
'data_class' => FormData2::class,
]);
}
}
class FormType3 extends AbstractType
{
public function buildForm(FormBuilderInterface $builder, array $options)
{
$builder
->add('field3')
->add('field4');
}
public function configureOptions(OptionsResolver $resolver)
{
$resolver->setDefaults([
'data_class' => FormData3::class,
]);
}
}
Here is the prototype:
<div {{ stimulus_controller('form-collection') }}
data-form-collection-index-value="{{ form.formType3|length > 0 ? form.formType3|last.vars.name + 1 : 0 }}"
data-form-collection-prototype-value="{{ form_widget(form.formType3.vars.prototype)|e('html_attr') }}" <<============
>
<ul {{ stimulus_target('form-collection', 'collectionContainer') }}></ul>
<button type="button" {{ stimulus_action('form-collection', 'addCollectionElement') }}>Add a tag</button>
</div>
In Stimulus Controller form-collection i get the prototype in this way
item.innerHTML = this.prototypeValue.replace(/__name__/g, this.indexValue);
The prototypeValue It return an empty string