[Django]-Django Writable Nested Serializers Update

Try this code into your AlmacenSerializer.

def update(self, instance, validated_data):
    item_data = validated_data.pop('item')
    medida_data = validated_data.pop('medida')
    sucursal_data = validated_data.pop('sucursal')

    item = instance.item
    for k, v in item_data.items():
        setattr(item, k, v)
    item.save()

    medida = instance.medida
    for k, v in medida_data.items():
        setattr(medida, k, v)
    medida.save()

    sucursal = instance.sucursal
    for k, v in sucursal_data.items():
        setattr(sucursal, k, v)
    sucursal.save()   

    instance.peso = validated_data.get('peso', instance.peso)
    instance.save()
    return instance