Django AttributeError при сохранении данных с помощью DRF

У меня проблема, когда я делаю POST. запись создается (я могу видеть ее в панели администратора django), но DRF выдает мне ошибку

AttributeError at /api/v1/reviews/

У объекта 'Review' нет атрибута 'review_score'

model.py

class Review(models.Model):
    company = models.ForeignKey(Company, related_name='company_review', on_delete=models.CASCADE)
    title = models.CharField(max_length=255)
    comments = models.TextField()
    validated = models.BooleanField(default=False)
    note_quality = models.DecimalField(max_digits=5, decimal_places=2)
    note_timing = models.DecimalField(max_digits=5, decimal_places=2)
    note_qualprix = models.DecimalField(max_digits=5, decimal_places=2)
    note_react = models.DecimalField(max_digits=5, decimal_places=2)
    note_followup = models.DecimalField(max_digits=5, decimal_places=2)
    note_clean = models.DecimalField(max_digits=5, decimal_places=2)

    created_at = models.DateField(auto_now_add=True)
    created_by = models.ForeignKey(User, related_name='created_review', on_delete=models.CASCADE)

    def __str__(self):
        return self.title

views.py

class ReviewViewSet(viewsets.ModelViewSet):
    serializer_class = ReviewSerializer
    queryset = Review.objects.all()

    def get_queryset(self):
        company_id = self.request.query_params.get('company_id', None)

        return self.queryset.filter(company_id=company_id, validated=True).annotate(
            review_score = Sum(F('note_quality')+F('note_timing')+F('note_qualprix')+F('note_react')+F('note_followup')+F('note_clean'))/6,
        )

    def perform_create(self, serializer):
        obj = serializer.save(created_by=self.request.user)

serializer.py

class ReviewSerializer(serializers.ModelSerializer):
    created_by = UserCreateSerializer(read_only=True)
    review_score = serializers.SerializerMethodField()

    def get_review_score(self, obj):
        rounded = round_up(obj.review_score, 0.5)        
        return rounded

    class Meta:
        model = Review
        read_only_fields = ('created_at'),
        fields = ('id','company','title','comments','validated','note_quality','note_timing','note_qualprix','note_react','note_followup','note_clean','created_at', 'created_by', 'review_score')

obj.save()

obj = serializer.save(created_by=self.request.user)