Night Hawk x10 R9000 hosting Plex connected to Synology NAS

I'm looking for some assistance please. I have Plex running on my x10. Firmware is all up to date. My media is on a Synology NAS. 

When I select Add Network Drive connection, I select the device from the drop down, copy and paste the folder name (/volume1/video), then add user name and password and click Apply. For some reason this fails and the page refreshes.

I presume it is a setting on the NAS that I’m missing? I can see the NAS files on my PC. I can't figure out why mapping the drive fails. I have seen similar issues in the forum but still stumped. Any assistance would be greatly appreciated. Thanks in advance.