I suppose you’re using http://<NAS.IP>:32400/web for step 1 of your observations? Did you by chance run this server before under a different Plex account? Also… considering you made the Plex share visible… I hope you didn’t story your media there!?
Plex
https://support.plex.tv/articles/204281528-why-am-i-locked-out-of-server-settings-and-how-do-i-get-in/
