Django Rest Framework - return user id and token after registration

The mistake is in the line

user = User.objects.filter(user=serializer.instance)

Firstly, there is no field named user on your User model. Secondly, you don't need to filter on the User model to get the created user as you already have the user with you in serializer.instance. So, there is no need for that line.

If you just want the id, you can get that using serializer.instance.id.

A neater solution is to depend on super()'s implementation:

    def create(self, request, *args, **kwargs):
        response = super().create(request, *args, **kwargs)
        token, created = Token.objects.get_or_create(user_id=response.data["id"])
        response.data["token"] = str(token)
        return response

And ensure "id" is included in your Serializer's fields:

class UserSerializer(serializers.ModelSerializer):

    class Meta:
        model = User
        fields = ["id", ...