I've set up a single GoCodes redirect with key 'qrcode'. The URL that is supposed to trigger the redirection, shown in the Manage GoCodes list under the key, is 'http://cg4tx.org/go/qrcode/'. The target URL is 'http://cg4tx.org'.
Visiting 'http://cg4tx.org' directly works perfectly.
Visiting 'http://cg4tx.org/go/qrcode/'' gets a 404 File Not Found.