Question: RAX120 Router and USB devices

I have an RAX120 Router - it’s amazing. But I would really like to get the ReadyCLOUD feature to work with my USB external hard drive (not SSD) 4TB - Seagate brand. But it will never show up as a USB device. Today I plugged in a different USB device. It’s a 500GB Samsung SSD, and it showed up immediately in ReadyCLOUD. Had anyone else experienced this? It would be a dream to get to use this 4TB EHD, because there is already a ton of files in there I would like to be able to access across my home network. -It’s possible that it’s not supported (although I don’t see anywhere that it’s NOT supported). -Or maybe I need to format the drive and try again (I really don’t want to do that because I would lose 3+ TB of data). Any advice would be super welcome.