500 Server Error When Using Foursquare API - php

Question

I'm using php-foursquare library for Foursquare API calls.
This is my index.php
require_once("FoursquareAPI.class.php");
$client_key = "blabla";
$client_secret = "blabla";
$redirect_uri = "http://localhost/4kare/index.php";
// ($redirected_uri equals to registered callback url)
// Load the Foursquare API library
$foursquare = new FoursquareAPI($client_key,$client_secret);
// If the link has been clicked, and we have a supplied code, use it to request a token
if(array_key_exists("code",$_GET)){
// example $_GET['code'] = FJRW1Z5TZ3H0E3Y2WN4Q0UPSH1PEIDADTZDHYKVG32DJTH2E
$token = $foursquare->GetToken($_GET['code'],$redirect_uri);
}
// If we have not received a token, display the link for Foursquare webauth
if(!isset($token)){
echo "<a href='".$foursquare->AuthenticationLink($redirect_uri)."'>Connect to this app via Foursquare</a>";
// Otherwise display the token
}else{
echo "Your auth token: $token";
}
But GetToken() method returning 500 server error . THis is source code of GetToken () method :
public function GetToken($code,$redirect){
$params = array("client_id"=>$this->ClientID,
"client_secret"=>$this->ClientSecret,
"grant_type"=>"authorization_code",
"redirect_uri"=>$redirect,
"code"=>$code);
$result = $this->GET($this->TokenUrl,$params);
$json = json_decode($result);
$this->SetAccessToken($json->access_token);
return $json->access_token;
}

Answer 1

I'm not using php-foursquare, but I faced a similar problem when using Guzzle to connect to 4sq REST endpoints.
It turns out that a request will result in an unhandled exception if you don't wrap it in a try catch block and it gets anything different than a 200 header. I couldn't understand why I was getting error 500, but when I captured and printed the exception it showed Foursquare returning a 401 with a much more informative msg. In my case, the redirecting URL had a typo.
try {
$result = $this->GET($this->TokenUrl,$params);
} catch (Exception $e) {
echo $e->getMessage();
}

Answer 2

Well, here is the problem. You don't have any control over 4square's servers, so you don't have enough information to go about this without guessing. I would do two things:
Google the API call you are using and see if it's a common problem with a commmon answer
Email 4square - it's their server spitting out an error message with no useful information.