Searching both Google and Bing show nothing relating to code500 or code 500 licenses on the DirectAdmin site. The term does, however, come up on other sites from time to time. probably an unsubstantiated and unreliable reference to Error 500 - Internal Server Error, but it certainly doesn't refer to an Internal License, and in any event, an Internal License is NOT a VPS license.
For anyone who needs information about special pricing for a VPS license you'll need to oopen an email dialogue with DirectAdmin Sales as they don't publish such information anywhere on the 'net.
And you get that information where? The only way you can be a reseller of DirectAdmin is to put it on servers you rent to others; you need to discuss that withDirectAdmin Sales.
And from where do you get the term code 500 license? It sure doesn't exist anywhere authoritative.
DirectAdmin does not have a reseller program, reselling is not allowed. They do however offer internal license, wich is for datacenters that is offering leased dedicated servers or vps. All other users must buy external licenses. All the information you need is here http://www.directadmin.com/pricing.html (Edit: I wrote my reply at same time as nobaloney, I did not see his reply before I posted.)