The onion address is connected to your start9 server? Do you have turn on the SOCKS proxy in 0xchat?
Discussion
I have tried that setting both on and off with still no better result. Yes, the .onion address is the address generated by the Nostr Relay on the Start9 server.
Are you trying to send a DM? If so, it will send messages to the counterpart’s DM relay list. If you can’t connect to the counterpart's DM relay list, the result will be a sending failure.
I have 2 phones with separate Nsec. Both connected the same way to the same servers. I should be able to send a DM from one phone to another via my private server. That’s what I think anyway. But it keeps failing. I have tried multiple settings, with Orbot on and off. If I use the supplied DM servers then the message goes through. Trying to use my private server fails.