Cannot connect to a port over the internet (works from localhost)

I’m running something on port 9292:

david@theta:~$ lsof -ni tcp:9292
COMMAND  PID  USER   FD   TYPE     DEVICE SIZE/OFF NODE NAME
ruby    2406 david   13u  IPv4 1579461398      0t0  TCP 127.0.0.1:9292 (LISTEN)

david@theta:~$ telnet localhost 9292
Trying 127.0.0.1...
Connected to localhost.
Escape character is '^]'.

The problem is that from elsewhere I cannot react it:

david@eclipse:~$ telnet 188.226.243.223 9292
Trying 188.226.243.223...
telnet: connect to address 188.226.243.223: Connection refused

Port 80 works:

david@eclipse:~$ telnet 188.226.243.223 80
Trying 188.226.243.223...
Connected to 188.226.243.223.
Escape character is '^]'.

I’m not using any firewalls.

What else can I try?

Thank you, David