Notification service 503 error

I’m setting up the notification service - installing on main BF server. After doing so, and executing configuration task successfully, unable to send emails successfully. Task completes successfully but no emails. Looking at logs, in the …/BES Server/Applications/Logs/ns-monitor-app.log file I see:

2019-05-02 13:01:37.244 - info: [MON004I] Beginning poll process by testing REST credentials …
2019-05-02 13:01:37.400 - info: [MON011I] Credentials are valid (successfully connected to the server REST API)
2019-05-02 13:01:37.400 - info: [MON009I] Polling BES server [servername redacted:42311] for notification request actions …
2019-05-02 13:01:39.744 - error: [MON010E] Failed to connect to the BES server. Status: [503], Msg: [Service Unavailable]

42311 is the proper port for our server.

Any ideas where to look? The server is working well otherwise.

Thanks.

did you ever get a solution to this, I am having the same issue