Ошибка при настройке модели и сериализатора django

У меня следующая ошибка в DRF (Django Rest Framework):

Internal Server Error: /book/book/
Traceback (most recent call last):
  File "/home/divyessh/Desktop/Projects/club-booking/booking-new/venv/lib/python3.8/site-packages/django/core/handlers/exception.py", line 47, in inner
    response = get_response(request)
  File "/home/divyessh/Desktop/Projects/club-booking/booking-new/venv/lib/python3.8/site-packages/django/core/handlers/base.py", line 181, in _get_response
    response = wrapped_callback(request, *callback_args, **callback_kwargs)
  File "/home/divyessh/Desktop/Projects/club-booking/booking-new/venv/lib/python3.8/site-packages/django/views/decorators/csrf.py", line 54, in wrapped_view
    return view_func(*args, **kwargs)
  File "/home/divyessh/Desktop/Projects/club-booking/booking-new/venv/lib/python3.8/site-packages/django/views/generic/base.py", line 70, in view
    return self.dispatch(request, *args, **kwargs)
  File "/home/divyessh/Desktop/Projects/club-booking/booking-new/venv/lib/python3.8/site-packages/rest_framework/views.py", line 509, in dispatch
    response = self.handle_exception(exc)
  File "/home/divyessh/Desktop/Projects/club-booking/booking-new/venv/lib/python3.8/site-packages/rest_framework/views.py", line 469, in handle_exception
    self.raise_uncaught_exception(exc)
  File "/home/divyessh/Desktop/Projects/club-booking/booking-new/venv/lib/python3.8/site-packages/rest_framework/views.py", line 480, in raise_uncaught_exception
    raise exc
  File "/home/divyessh/Desktop/Projects/club-booking/booking-new/venv/lib/python3.8/site-packages/rest_framework/views.py", line 506, in dispatch
    response = handler(request, *args, **kwargs)
  File "/home/divyessh/Desktop/Projects/club-booking/booking-new/venv/lib/python3.8/site-packages/rest_framework/generics.py", line 190, in post
    return self.create(request, *args, **kwargs)
  File "/home/divyessh/Desktop/Projects/club-booking/booking-new/venv/lib/python3.8/site-packages/rest_framework/mixins.py", line 20, in create
    headers = self.get_success_headers(serializer.data)
  File "/home/divyessh/Desktop/Projects/club-booking/booking-new/venv/lib/python3.8/site-packages/rest_framework/serializers.py", line 548, in data
    ret = super().data
  File "/home/divyessh/Desktop/Projects/club-booking/booking-new/venv/lib/python3.8/site-packages/rest_framework/serializers.py", line 246, in data
    self._data = self.to_representation(self.instance)
  File "/home/divyessh/Desktop/Projects/club-booking/booking-new/venv/lib/python3.8/site-packages/rest_framework/serializers.py", line 515, in to_representation
    ret[field.field_name] = field.to_representation(attribute)
  File "/home/divyessh/Desktop/Projects/club-booking/booking-new/venv/lib/python3.8/site-packages/rest_framework/fields.py", line 1368, in to_representation
    return value.isoformat()
AttributeError: 'SlotChoice' object has no attribute 'isoformat'

Ниже приведен мой serializer.py для резервирования:

from rest_framework import serializers
from .models import Booking
from court.serializers import CourtSerializer
from users.models import User
from slots.models import SlotChoice
from datetime import date


class BookingSerializer(serializers.ModelSerializer):
    date = serializers.DateField(
            required=True,
            )
    user = serializers.EmailField(required=True)
    court = CourtSerializer
    slot = serializers.TimeField(required=True)

    class Meta:
        model = Booking
        fields = ('court','user','date', 'slot')

    def validate(self, attrs):
        d = attrs['date']
        now = date.today()
        if d <= now:
            raise serializers.ValidationError("Date is too old")

        s = attrs['slot']
        if len(SlotChoice.objects.filter(slot=s)) < 1:
            raise serializers.ValidationError("Not an appropriate time slot")

        return attrs


    def create(self, validated_data):
        slot = SlotChoice.objects.filter(slot=validated_data['slot'])[0]
        booking= Booking.objects.create(
            slot= slot,
            date=validated_data['date'],
            court=validated_data['court'],
            user=User.objects.filter(email=validated_data['user'])[0]
        )
        booking.save()
        return booking

и мои модели:

slots ( models.py )

class SlotChoice(models.Model):
    slot = models.TimeField('slot', unique=True)

бронирование (models.py)

from django.db import models
from users.models import User
from court.models import Court
from slots.models import SlotChoice

class Booking(models.Model):
    class Meta:
        constraints = [
            models.UniqueConstraint(fields=['court', 'date', 'slot'], name="unique_slot")
        ]
    user = models.ForeignKey(User, on_delete=models.CASCADE)
    court = models.ForeignKey(Court, on_delete=models.CASCADE)
    date = models.DateField('date')
    slot = models.ForeignKey(SlotChoice, on_delete = models.CASCADE)

Я попробовал несколько решений на SO, но не смог решить эту ошибку. Пожалуйста, помогите мне справиться с этой ошибкой. Любая помощь будет оценена по достоинству.

class BookingSerializer(serializers.ModelSerializer):
    ...
    slot = serializers.TimeField(required=True)
    ...

class Booking(models.Model):
    ...
    slot = models.ForeignKey(SlotChoice, on_delete = models.CASCADE)
    ...

class BookingSerializer(serializers.ModelSerializer):
    ...
    slot = SlotChoiceSerializer()
    # or something like ↓ (I'm not familiar with this stuff, so check links below to get details)
    # slot = serializers.StringRelatedField(many=False)
    ...

# where SlotChoiceSerializer is
class SlotChoiceSerializer(serializers.ModelSerializer):
    ...
    slot = serializers.TimeField(required=True)
    ...
    class Meta:
        model = SlotChoice
    ...