Global citizen and extremist.
I have the same question and can't find an answer online. Apple doesn't ship them with less than 3 populated.
I had to use Disk Utility to partition the drive and then it showed fine. Rookie mistake.
The replacement hard drive I used doesn't even appear to spin up and the Time Capsule restore process doesn't show it as available. It just stays at Searching for disks and never finds it.