Error "You don't have permission to access / on this server." when deploy on Heroku?

I have deployed my laravel 5.4 app on Heroku. The problem is, I am getting this error message:

Forbidden You don't have permission to access / on this server

My Procfile:

web: vendor/bin/heroku-php-apache2 public/

My composer.json

     "post-install-cmd": [
         "php artisan clear-compiled",
         "php artisan optimize",
         "chmod -R 777 public/"
     ]

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