Почему этот вложенный сериализатор (ForeignKey) не работает?

class RFIDReaderSerializer(serializers.HyperlinkedModelSerializer):
    class Meta:
        model = RFIDReader
        bind_state_choice = ProductEntityStateChoiceSerializer()
        # depth = 2
        fields = (
            "url", "pk", "reader_name", "reader_host", "reader_address", "reader_ip", "reader_port",
            "bind_state_choice",
            "bind_state_location"
        )

Сериализатор

Вложенный сериализатор

График модели

RestFul

class RFIDReaderSerializer(serializers.HyperlinkedModelSerializer):
    bind_state_choice = ProductEntityStateChoiceSerializer()

    class Meta:
        model = RFIDReader
        # depth = 2
        fields = (
            "url", "pk", "reader_name", "reader_host", "reader_address", "reader_ip", "reader_port",
            "bind_state_choice",
            "bind_state_location"
        )