Can't use valid Server Identifier as Referrer

[HoLyCoW]

I help manage a clan's server that is hosted here with NFO.

I now want to set up my own account to manage a personal game server for myself. When signing up, I'm asked for a Referrer. I figured it would be a chance for me to help out the clan, so I wanted to put them down as a referrer. At first, I typed in their Control Panel login email, but then I was shown a message saying that it has to be a valid server identifier.

So I logged into their control panel, and saw the name of their identifier. When I go to type it in, and hit "request server rental", I still get the same error saying that it's not a valid server identifier. How can this be if it shows up in their control panel?!?

The server identifier is: hk

[edit]
The error I'm getting is:

An error was encountered when processing your order.

You specified an invalid referrer. The referrer must be the identifier of an active existing server. If you are unsure of the identifier of the server (for instance, if you only know its name or IP address), you will need to ask the renter of that server for his identifier.

When you're ready, please close this window and resubmit your order.

[kraze]

Our referral system is not yet cross service compatible. Meaning that for a referral to work both parties must have the same service. I.E game to game and voice to voice.

[HoLyCoW]

Well the clan has a game server and I'm trying to add a game server.

[kraze]

It is a game server but the base package is a VDS. It has to solely be a game server.

[HoLyCoW]

Ah, okay. Thanks!