External HDD not visible for PR4100

WD External and Portable SSD External SSD for macOS
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I’m hoping that I post this in the right channel. Does anyone manage to make their external HDD work with PR4100 by simply attaching to any USB port NAS has?
I have Seagate 3TB Flex Go and when I plug it doesn’t recognize it. On my Mac (direct connection with USB), there are no issues. Any help will be appreciated. Does it need to be in certain format to be visible? And yes, I’m in latest software for NAS as well as using My Cloud 5 for web access. Thank you in advance.