Here's the Apex REST class:

@RestResource(urlMapping='/abc/def/*')
global with sharing class TheRESTclass
{
  @HttpGet
  global static String doGet(RestRequest req, RestResponse res)
  { return 'hello'; }
}

From the Apigee Salesforce console, I call the following URL (using OAuth authentication):

https://na7.salesforce.com/services/apexrest/abc/def

I've also tried it with the namespace in there:

https://na7.salesforce.com/services/apexrest/namespace/abc/def

But I keep getting this error:

 "message": "Could not find a match for URL /namespace/abc/def", "errorCode": "NOT_FOUND"

I've looked at multiple tutorials and they all guided me in the same direction. So I don't know what I could be possibly missing. Do I need to comfigure Remote Site Settings or do any other type of configuration?

Thanks in advance.