Find the error in this webhook registration endpoint snippet:

Find the error in this webhook registration endpoint snippet:
@app.route('/register', methods=['POST'])
def register():
  data = request.get_json()
  if 'callback_url' not in data:
    return {'error': 'callback_url required'}, 400
  callback = data['callback_url']
  if not callback.startswith('http'):
    return {'error': 'Invalid URL'}, 400
  return {'message': 'Registered'}, 201