Error 404 on a POST request from Ajax to Flask

from flask import Flask, render_template, request

app = Flask(__name__, template_folder='templates')

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

@app.route('/', methods=["POST"])
def post():
    print(request.data)
    try:
        data = request.json
    except Exception as e:
        data = {'error': repr(e)}
    return data

if __name__ == "__main__":
    app.run(debug=True)

$.ajax({
  method: 'POST',
  url: '/',
  data: {'lat': 12.3, 'lon': 45.6},
  contentType: 'application/json',
  success: function(res){console.log(res);}
})

b'lat=12.3&lon=45.6'

{'error': ""}

$.ajax({
  method: 'POST',
  url: '/',
  data: JSON.stringify({'lat': 12.3, 'lon': 45.6}),
  contentType: 'application/json',
  success: function(res){console.log(res);}
})

b'{"lat":12.3,"lon":45.6}'

{lat: 12.3, lon: 45.6}