Callback URL isn't working

[ChrGriffin]

I'm instantiating my Shapeways client like so:

$client = new ShapewaysClient(
    '<CONSUMER KEY>', // consumer key
    '<CONSUMER SECRET>', // consumer secret
    <CALLBACK URL>, // callback URL
    $request->session()->get('shapeways_client_token'), // oauth token
    $request->session()->get('shapeways_client_secret') // oauth secret
);

However after being clicking 'Authorize' on the Shapeways oauth page, I'm not being redirected back to the callback URL, I'm being redirected back to the Shapeways oauth page, over and over.