A setting called “DNS Rebind Protection” which is normally auto-enabled in router could impact Plex’s download feature. Plex would throw errors such as Error 409 or Failed to download.
In order to fix it, we need to either completely disable the DNS Rebind Protection in our router which is quite often not recommended because of security risks. Instead, we can add an exception, entry for
plex.direct or the IP Address of the Plex server.
Adding an entry in my current router was not possible, however, adding an exception for an IP Address is allowed.