This Flask code snippet is intended to turn GPIO pin 18 ON or OFF via web requests:

This Flask code snippet is intended to turn GPIO pin 18 ON or OFF via web requests:

from flask import Flask
import RPi.GPIO as GPIO

app = Flask(__name__)
GPIO.setmode(GPIO.BCM)
GPIO.setup(18, GPIO.OUT)

@app.route('/pin18/')
def control_pin(state):
    if state = 'on':
        GPIO.output(18, GPIO.HIGH)
        return 'Pin 18 ON'
    elif state == 'off':
        GPIO.output(18, GPIO.LOW)
        return 'Pin 18 OFF'
    else:
        return 'Invalid'

What is the error in this code?