Not sure which port to run your service on?

Quick answer, with the reasons:

→ Use 443 (HTTPS). It works from almost every network.
→ Use TCP, not UDP. TCP resends lost data on a bad connection; UDP drops it.
→ Need UDP or an unusual port? Pick a region where all ports are open.
→ Test before you trust it: nc -zv YOUR_SERVER_IP 443

A running service on a blocked port looks exactly like a dead one. Here's how to tell them apart:

https://www.doprax.com/docs/which-ports-protocols-survive-bad-network