Django: Generic detail view must be called with either an object pk or a slug

Question

Getting this error when submitting the form associated with this view. Not sure what exactly is the problem, considering I have a form with a very similar structure and it works

Answer 1

I am using Django version 2.2.12,

Here is just another example this works fine for me :

models.py

from django.db import models

class Book(models.Model):
    title = models.CharField(max_length=256)
    author = models.CharField(max_length=256)
    pages = models.IntegerField()
    price = models.FloatField()

views.py

from django.views.generic import ListView,DetailView
from testapp.models import Book

class BookListView(ListView):
    model=Book

class BookDetailView(DetailView):
    model=Book

urls.py

from django.contrib import admin
from django.urls import path
from testapp import views

urlpatterns = [
    path('admin/', admin.site.urls),
    path('', views.BookListView.as_view()),
    path('/', views.BookDetailView.as_view()),
]