Unable to get callback function to work (Guzzle issues)

[max-x-1000000]

Just in case anyone else has been having issues getting this to run out of the box on Windows:

1. Update Composer
2. Download the latest Xero-php-oauth2 release from here:
   https://github.com/XeroAPI/xero-php-oauth2/releases
3. Download the latest release of this fork and extract everything into the same directory as 2 above, except the composer.json and composer.lock files
4. Install as per the instructions in the readme (composer install) & assigning the clientId, clientSecret and redirectUri for authorization.php, authroizedResource.php and callback.php - make sure these match you redirectUri in your app settings (https://developer.xero.com/app/manage/app)
5. Should run fine now