How to bind nested data on livewire when using checkbox?

Im try using checkbox in livewire 2.x, its ok when using single property. But its not worked when using nested property.

blade :

@foreach ($questions as $key => $question)
    <div class="card card-primary">
        <div class="card-body">
            <div class="section-title mt-0">{{ $question->description }}</div>
            <div class="form-group">
                @foreach ($question->choices as $choice)
                    <div class="form-check form-check-inline col-12 col-md-5 col-lg-5">
                        <input
                            class="form-check-input"
                            type="checkbox"
                            id="checkbox-choice-{{ $choice->id }}"
                            value="{{ $question->id }}_{{ $choice->id }}"
                            wire:model.defer='answers.{{ $key }}.choices'
                        >
                        <label class="form-check-label" for="checkbox-choice-{{ $choice->id }}">{{ $choice->description }}</label>
                    </div>
                @endforeach
            </div>
        </div>
    </div>
@endforeach

then on component :

public $answers = [];

public $rules = [
    'answers' => 'required|array|min:1',
];

public function submitAnswers()
{
    /** @var array $validData */
    $validData = $this->validate();
    Log::info('' . json_encode($validData));

}

example result :

{"answers":[{"choices":"42_167"}]}

property choices only returns a string result even though it has selected multiple choices, how to make property choices an array?