Facebook PHP SDK error mb_substr

Question

I am following this code for my fb app . I host this app on Heroku. When I login its shows this error :

Fatal error: Call to undefined function Facebook\\mb_subs         


        

Answer 1

You need to enable the mbstring extension: https://devcenter.heroku.com/articles/php-support#extensions

In your composer.json, the require block needs to contain it, like so:

{
  "require": {
    "ext-mbstring": "*"
  }
}