(I am new to Django Rest Framework and Django in general)

I have a Beer model that looks like this:

class Beer(models.Model):
    id = models.BigAutoField(primary_key=True)
    name = models.CharField(max_length=255)
    brewery = models.ForeignKey(Brewery, on_delete=models.CASCADE)
    beer_type = models.ForeignKey(BeerType, on_delete=models.PROTECT)

    class Meta:
        db_table = "beer"

I then specify a BeerSerializer like this:

class BeerSerializer(serializers.ModelSerializer):
    brewery = BrewerySerializer()
    beer_type = BeerTypeSerializer()

    class Meta:
        model = Beer
        fields = ['id', 'name', 'brewery', 'beer_type']

    def create(self, validated_data):
        brewery_data = validated_data.pop('brewery')
        beer_type_data = validated_data.pop('beer_type')
        beer = Beer.objects.create(**validated_data)
        beer.brewery = Brewery.objects.get_or_create(**brewery_data)
        beer.beer_type = BeerType.objects.get_or_create(**beer_type_data)
        return beer

And a BeerViewSet:

class BeerViewSet(viewsets.GenericViewSet):
    permission_classes = [permissions.IsAuthenticated]
    serializer_class = BeerSerializer

...
    def create(self, request):
        pdb.set_trace()
        serializer = self.get_serializer(data=request.data)
        serializer.is_valid(raise_exception=True)
        serializer.save()
        return Response(serializer.data, status=status.HTTP_201_CREATED)

(I’ve left out the list and retrieve implementations in the ViewSet)

When I then make a POST request from my app to /api/beers/ with the following JSON:

{
    "beer_type": {
        "id": 154,
        "name": "Beer Type 1"
    },
    "brewery": {
        "country": "c1",
        "id": 929,
        "location": "l1",
        "name": "Brewery1"
    },
    "name": "Beer1"
}

I get an error with code 400 and error body:

{
    "beer_type": {
        "name": [
            "beer type with this name already exists."
        ]
    }
}

This is technically true, but what am I doing wrong if I want to allow a POST creating a new Beer object, which references an existing BeerType object (and I guess I would have the same problem with the Brewery reference)?