Why is RetrieveUpdateDestroyAPIView not working?

Question

RESTful API

#settings
INSTALLED_APPS = [
    'django.contrib.admin',
    'django.contrib.auth',
    'django.contrib.contenttypes',
    'django.contrib.sessions',
    'django.contrib.messages',
    'django.contrib.staticfiles',

    'rest_framework',

    'posts.apps.PostsConfig',
]

REST_FRAMEWORK = {
    'DEFAULT_PERMISSION_CLASSES': [
        'rest_framework.permissions.AllowAny',
    ]
}

#blog_project_urls
from django.conf.urls import url,include
from django.contrib import admin

urlpatterns = [
    url('api', include('posts.urls')),
    url('admin/', admin.site.urls),
]
#post_url
from django.conf.urls import url
from .views import (
    PostListView,
    PostDetailView
)

urlpatterns=[
    url('/<int:pk>/', PostDetailView.as_view()),
    url(' ',PostListView.as_view())
]

#post_view
from django.shortcuts import render
from .serializers import PostSerializer
# Create your views here.
from .models import Posts
from rest_framework import generics

class PostListView(generics.ListCreateAPIView):
    queryset=Posts.objects.all()
    serializer_class=PostSerializer

class PostDetailView(generics.RetrieveUpdateDestroyAPIView):
    queryset=Posts.objects.all()
    serializer_class=PostSerializer

# post_serializers
from rest_framework import serializers
from .models import Posts


class PostSerializer(serializers.ModelSerializer):
    class Meta:
        model=Posts
        fields=('id', 'author', 'title', 'body', 'created_at',)

#post_models 
from django.db import models
from django.contrib.auth.models import User


class Posts(models.Model):
    author=models.ForeignKey(
        User,
        on_delete=models.CASCADE
    )
    title=models.CharField(max_length=200)
    body=models.TextField()
    created_at = models.DateTimeField(auto_now_add=True)
    updated_at=models.DateTimeField(auto_now=True)

    def __str__(self):
        return self.title

The crux of the matter is that , does not prehead on the api// link. Class PostDetailView(generics.RetrieveUpdateDestroyAPIView) does not work. Help please