bitly not shortening url on server machine

I am usin开发者_如何学Cg the bitbly API to shorten urls.

here is a snippet of the PHP code I am using.

<?php
        $bitly = 'http://api.bit.ly/shorten?version='.$version.'&longurl='.urlencode($url).'&login='.$login.'&apikey='.$appkey.'&format='.$format;

        //The above string evaluates to:
http://api.bit.ly/shorten?version=&longurl=http://real.address.replace&login=myname&apikey=A_key_provided_by_bitbly&format=json

        $response = file_get_contents($bitly);

        $json = @json_decode($response,true);
}

When I invoke this, I get the following JSON response:

{"errorCode": 500, "errorMessage": "MISSING_ARG_APIKEY", "results": null, "statusCode": ""}

I can't for the life of me, understand why bitly is returning that error - especially since I am passing the api key - what gives?

The parameter is apiKey, not apikey.