Kept getting werkzeug.routing.BuildError - python-3.x

Question

I tried running the code and got this werkzeug.routing.BuildError: Could not build url for endpoint 'book'. Did you mean 'sign_in' instead?
Also, if i try to access the /main route, it says URL not found on server. Can somebody please help me.
import os
import csv
from flask import Flask, session, render_template, request
from flask_session import Session
from sqlalchemy import create_engine
from sqlalchemy.orm import scoped_session, sessionmaker
app = Flask(__name__)
# Check for environment variable
if not os.getenv("DATABASE_URL"):
raise RuntimeError("DATABASE_URL is not set")
# Configure session to use filesystem
app.config["SESSION_PERMANENT"] = False
app.config["SESSION_TYPE"] = "filesystem"
Session(app)
# Set up database
engine = create_engine(os.getenv("DATABASE_URL"))
db = scoped_session(sessionmaker(bind=engine))
f = open("books.csv")
reader = csv.reader(f)
for isbn, title, author, year in reader:
db.execute("INSERT INTO books (ISBN, title, author, year) VALUES (:ISBN, :title, :author, :year)",
{"ISBN": isbn, "title": title, "author": author, "year": year})
print(f"Added flight from {isbn} to {year} lasting {title} minutes.")
db.commit()
#app.route("/")
def sign_in():
return render_template("Sign.html")
#app.route("/main" method = "POST")
def book():
name = request.form.get("name")
return render_template("books.html", username=name)
This is the sign.html document
{% extends "layout.html" %}
{% block title %}Sign in{% endblock %}
{% block body %}
<div class="main">
<p class="sign" align="center">Sign in</p>
<form action= "{{ url_for('book') }}" class="form1" method="post">
<input name = "name" class="un " type="text" align="center" placeholder="Username">
<input class="pass" type="password" align="center" placeholder="Password">
<button class="submit" align="center">Sign in</button>
</form>
</div>
{% endblock %}
This is the books.html document
{% extends "layout.html" %}
{% block title %} {{username}} {% end block%}
{% block body%}
{% end block %}

Answer 1

#app.route("/main" method = "POST")
There are two things wrong with this line:
no comma after "/main" (it should cause syntax error, so I assume it just got lost in the snippet)
allowed methods for an endpoint are defined with keyword argument methods, as a iterable of strings, so in your code it should go like methods = ["POST"] instead of method = "POST".
However, in newest version of Flask (1.1.2), the second issue should cause TypeError, so maybe you're using some older version which doesn't handle such case and the result is that the endpoint doesn't exist.