Dropbox WebAuth: Missing CSRF token in session

I am trying to follow this basic example: http://dropbox.github.io/dropbox-sdk-php/api-docs/v1.1.x/class-Dropbox.WebAuth.html But I after I click "Allow" on the dropbox site, I keep getting Missing CSRF token in session when I get redirected back to /finish.

Here is the code I am working with:

public function start()
{   
    $authorizeUrl = $this->getWebAuth()->start();

    return redirect()->away($authorizeUrl);
}

public function finish()
{       
    $test = $this->getWebAuth()->finish($_GET);
    
    dd($test);
}

private function getWebAuth()
{   
    $appKey = 'key';
    $appSecret = 'secret';
    $appName = 'name';
    $appRedirect = 'http://example.com/finish';

    $appInfo = new Dropbox\AppInfo($appKey, $appSecret);
    $csrfTokenStore = new Dropbox\ArrayEntryStore($_SESSION, 'dropbox-auth-csrf-token');
    $webAuth = new Dropbox\WebAuth($appInfo, $appName, $appRedirect, $csrfTokenStore);

    return $webAuth;
}