validate_on_submit not working

####### views.py #######
from myapp import app
import flask
from forms import InventoryForm, LoginForm

@app.route('/login', methods=['POST', 'GET'])
def login():
    form = LoginForm()
    if form.validate_on_submit():
        return flask.redirect('/index')
    return flask.render_template('login.html', form=form)

@app.route('/', methods=['GET', 'POST'])
@app.route('/index', methods=['GET', 'POST'])
def index():
    return flask.render_template('index.html')

####### forms.py #######
from flask_wtf import FlaskForm
from wtforms import StringField, PasswordField, BooleanField, SubmitField
from wtforms.validators import DataRequired, InputRequired, Email, Length

class LoginForm(FlaskForm):
    email = StringField('email', validators=[InputRequired(), Email(), Length(max=40)])
    password = PasswordField('password', validators=[InputRequired()])
    remember = BooleanField('remember me')
    submit = SubmitField('submit')


####### login.html #######
<!DOCTYPE html>
<html>
<head>
  <title>Ansible UI</title>

  <!-- Latest compiled and minified CSS -->
  <link rel="stylesheet" href="https://maxcdn.bootstrapcdn.com/bootstrap/3.3.7/css/bootstrap.min.css" integrity="sha384-BVYiiSIFeK1dGmJRAkycuHAHRg32OmUcww7on3RYdg4Va+PmSTsz/K68vbdEjh4u" crossorigin="anonymous">
  <!-- Custom styles for this template -->
  <link href="/static/css/login.css" rel="stylesheet">
</head>

<body>

<div class="container">

   <form class="form-signin" action="/index" method="POST">
     {{ form.hidden_tag() }}
     <h2 class="form-signin-heading">Please sign in</h2>
     {{ form.email.label(class_="sr-only", for="inputEmail") }} {{ form.email(class_="form-control", id="inputEmail", placeholder="Email address")}}
   </br>
     {{ form.password.label(class_="sr-only", for="inputPassword") }} {{ form.password(class_="form-control", id="inputPassword", placeholder="Password") }}
     <div class="checkbox">
       <label>
         {{ form.remember(type="checkbox", value="remember-me") }} Remember me
       </label>
     </div>
     {{ form.submit(class_="btn btn-lg btn-primary btn-block", value="Sign in") }}
   </form>

 </div> <!-- /container -->
</body>
</html>