Djangoで CreateViewにおいて送信後、画面が遷移されない

DjangoにてTemplateViewを使って、サイト構築中です。

Createviewで、Reverselazy後に設定したパターンネームが違っているのかエラーが出ます。

データに書き込まれているので、データ送信までは確認できました。
その後、画面遷移でエラーが起きています。
appname:indexとしていますが、"逆引き名が違う"と遷移先に行きません。

Python
エラー文

NoReverseMatch at /post_create/
Reverse for 'index' not found. 'index' is not a valid view function or pattern name.
Request Method:	POST
Request URL:	http://127.0.0.1:8000/post_create/
Django Version:	3.0.4
Exception Type:	NoReverseMatch
Exception Value:	
Reverse for 'index' not found. 'index' is not a valid view function or pattern name.

Python
base.html

{% load static %}
<!DOCTYPE html>
<html lang="ja">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <link href="https://cdn.jsdelivr.net/npm/bootstrap@5.0.0-beta1/dist/css/bootstrap.min.css" rel="stylesheet" integrity="sha384-giJF6kkoqNQ00vy+HMDP7azOuL0xtbfIcaT9wjKHr8RbDVddVHyTfAAsrekwKmP1" crossorigin="anonymous">
    <script src="https://cdn.jsdelivr.net/npm/bootstrap@5.0.0-beta1/dist/js/bootstrap.bundle.min.js" integrity="sha384-ygbV9kiqUc6oa4msXn9868pTtWMgiQaeYH7/t7LECLbyPA2x65Kgf80OJFdroafW" crossorigin="anonymous"></script>
    <link rel="stylesheet" type="text/css" href="{% static 'app/style.css' %}">
</head>
<body>
    <nav class="navbar navbar-expand-lg navbar-light bg-light">
        <div class="container-fluid">
          <a class="navbar-brand" href="/">Home</a>
          <button class="navbar-toggler" type="button" data-bs-toggle="collapse" data-bs-target="#navbarNavAltMarkup" aria-controls="navbarNavAltMarkup" aria-expanded="false" aria-label="Toggle navigation">
            <span class="navbar-toggler-icon"></span>
          </button>
          <div class="collapse navbar-collapse" id="navbarNavAltMarkup">
            <div class="navbar-nav">
                <a class="nav-link active" aria-current="page" href="{% url 'app:post_create' %}">Tweet</a>

            </div>
          </div>
        </div>
      </nav>

        <div class="container">
 
        <div class="card">
                    {% block content %}
                    {% endblock %}
            </div>
        </div> 
    </div>
</div>
</body>
</html>

Python
index.html

{% extends 'app/base.html' %}
{% load static %}


{% block content %}
<h1 style="text-align:center; color:white; background-color:skyblue;">{% block title %}Time_Line_Site{% endblock%}</h1>
    {% for tweet in tweet_list %}
            <div class="row">
                <div class="col">
                    <div class="cardbody">
                    <div class="card-title"><strong>@{{tweet.name}}</strong></span>
                        <span>{{tweet.created_at}}</span>
                        <div class="mx-auto" style="width: 500px;">
                            <div class= "card-text">{{ tweet.tweet|linebreaksbr }}</div> 
                        </div>
                        <div class="border-bottom"></div>
                    </div>
                    </div>
                </div>

    {% endfor %}
{% endblock%}

Python
post_create.html

{% extends 'app/base.html' %}
{% load static %}


{% block content %}
    <form action="" method="post">
    {% csrf_token %}
    {{ form.as_p }}
    <div class="input-group">
          <button type="submit" class="btn btn-primary" >Add New</button>
      </div>
    </form>
  {% endblock%}

Python
urls.py

from django.urls import path

from .views import IndexView, PostCreateView
from . import views
app_name = "app"

urlpatterns = [
    path("",IndexView.as_view(template_name= "app/index.html")),
    path("post_create/",PostCreateView.as_view(),name="post_create"),
]

Python
views.py

from django.contrib.messages.api import success
from django.views.generic import ListView,TemplateView, CreateView
from django.shortcuts import render
from .models import User
from django.contrib import messages
from django.urls import reverse_lazy


class IndexView(ListView):
    model = User
    template_name = "index.html"
    context_object_name = 'tweet_list'
    paginate_by = 10


class PostCreateView(CreateView):
    model = User
    template_name = "app/post_create.html"
    fields = '__all__'
    success_url = reverse_lazy("app:index")