How to serialize a one to many relation in django-rest using Model serializer?

I figured it out. There were two errors.

Changed this:

class AskedToSerializer(serializers.ModelSerializer):
    class Meta:
        model = AskedTo
        fields = ('to_user', 'answered')

to this (notice the change in fields, fields on model and serializer didn't match)

class AskedToSerializer(serializers.ModelSerializer):
    class Meta:
        model = AskedTo
        fields = ('to_user', 'replied')

Secondly, I needed to define any extra fields outside class Meta

class QuestionSerializer(serializers.ModelSerializer):
    places = PlaceSerializer(many=True, required=False)
    asked = AskedToSerializer(source='askedto_set', many=True)    

    class Meta:
        model = Question
        fields = ('id', 'created_on', 'title', 'places', 'answered','asked')
        extra_kwargs = {'created_by': {'read_only': True}}

Notice the change in definition of places and asked.

In my case, I have this models.py:

class Section(models.Model):
     title = models.CharField(max_length=500)
     description = models.TextField(blank=True)
     user = models.ForeignKey(Profile, related_name="sections", on_delete=models.CASCADE)

class Feed(models.Model):
     title = models.CharField(max_length=500)
     link_rss = models.URLField(max_length=500)
     link_web = models.URLField(max_length=500)
     description = models.TextField(blank=True)
     language = models.CharField(max_length=50, blank=True)
     logo = models.URLField(blank=True)

     sections = models.ManyToManyField(Section, related_name="feeds")

And I completed the serializers.py this:

class FeedSerializer(serializers.ModelSerializer):
     sections = serializers.PrimaryKeyRelatedField(many=True, read_only=True)

     class Meta:
         model = Feed
         fields = '__all__'


class SectionSerializer(serializers.ModelSerializer):
     feeds = FeedSerializer(many=True, read_only=True)

     class Meta:
         model = Section
         exclude = ('user',)