FedEx Tracking API Response: 404

Question

Here is the situation.

I have a Rest API Tracking setup trying to get the status of the FedEx package.

Here is my code:

   $url = 'https://apis-sandbox.fedex.com/track/v1/123456789012';

   $api = new App_ApiTransaction('POST', $url, '', App_ApiTransaction::ENCODE_JSON);
   $api->addHeader( 'Authorization', 'Bearer '.$accessToken->accessToken);
   $api->addHeader( 'X-locale', 'en_US');
   $api->addHeader( 'Content-Type', 'application/json');

Why would I be getting a 404 response code?

Thank you, Kevin