Django Select a valid choice. That choice is not one of the available choices при создании формы

Не знаю как сделать так чтобы форма работала

forms.py

from django import forms
from .models import *


class PostForm(forms.ModelForm):
    class Meta:
        model = Post
        fields = ['title', 'posts', 'category']

        widgets = {
            'title': forms.TextInput(attrs={'class': 'form-control'}),
            'posts': forms.Textarea(attrs={'class': 'form-control'}),
            'category': forms.SelectMultiple(attrs={'class': 'form-control'}),
        }

Views.py

from django.views import View
from django.shortcuts import render, redirect
from .models import *
from .forms import PostForm
# Create your views here.

def main(request):
    posts = Post.objects.all()
    context = {'posts': posts}
    return render(request, 'blogs/main.html', context)

def postPage(request, title):
    post = Post.objects.get(title__iexact=title)
    context = {'post': post}
    return render(request, 'blogs/post_page.html', context)


class CreatePost(View):
    def get(self, requests):
        form = PostForm()
        return render(requests, 'blogs/post_editing.html', context={'form': form})

    def post(self, requests):
        bound_form = PostForm(requests.POST)
        if bound_form.is_valid():
            new_post = bound_form.save()
            return redirect(new_post)
        return render(requests, 'blogs/post_editing.html', context={'form': bound_form})

Urls.py

from django.urls import path
from .views import *

urlpatterns = [
    path('', main, name='main'),
    path('post_page/<str:title>/', postPage, name='postPage'),
    path('create_post/', CreatePost.as_view(), name='createPost'),
]

models

from django.db import models
from django.contrib.auth.models import User
# Create your models here.


class Category(models.Model):
    name = models.CharField(max_length=255, verbose_name='Имя категории')
    category_balls = models.FloatField()
    slug = models.SlugField(unique=True)

    def __str__(self):
        return self.name





class Author(models.Model):
    user = models.OneToOneField(User, null=True, blank=True, on_delete=models.CASCADE)
    email = models.CharField(max_length=122, null=True, verbose_name='Email')
    first_name = models.CharField(max_length=225, null=True, verbose_name='Имя')
    last_name = models.CharField(max_length=255, null=True, verbose_name='Фамилия')
    avatar = models.ImageField(upload_to='photos/%Y/%m/%d/', verbose_name='Изображение')


    def __str__(self):
        return self.first_name


class Post(models.Model):
    title = models.CharField(max_length=1000, verbose_name='Название блога')
    category = models.ForeignKey(Category, on_delete=models.CASCADE, verbose_name='Категория', blank=True)
    author = models.ForeignKey(Author, on_delete=models.CASCADE, verbose_name='Автор')
    posts = models.CharField(max_length=5000, verbose_name='Тело блога')
    time_publicaton = models.DateTimeField(auto_now_add=True, verbose_name='Время публикации')

    def __str__(self):
        return self.title