I tried entering it manually, but when it actually sent the information to the device, it returned the same error.
I think I just found a work around, though. Instead of doing particle setup, I first did particle serial wifi on the terminal. I was able to connect the photon to the wifi network, but it wasn't claimed on my account. I then put the photon back into setup mode, and ran particle setup. This time, setup went through without any errors and I was able to set it up (in this case, I did NOT enter my Wi-Fi network configuration manually, it was able to pick it up). Once I completed this setup, it appeared as claimed in my particle app (without a name). So... I didn't quite find a "solution," but I was able to register my device.