(Programming) Remote connections not coming through [solved]

[Dancso]

Hey, super off topic but there are some smart people frequenting this forum and I'm REALLY desperate for help.

I've written an app using C#/.NET using this wrapper https://github.com/nxrighthere/ENet-CSharp which builds on a networking library called ENet http://enet.bespin.org/
(Also using a thing called NetStack for (de)serialization but afaik that shouldn't be related to blocking connections)

In short, local connections work just fine, but remote ones don't. Tried various other machines (2 of my associates computers, and Amazon Linux 1/2 & Windows Server 2019 cloud VMs). Firewalls disabled, port forwarding working on same port using other apps. Port is IN USE by my app (blocks other apps from using said port) but is not listening (according to Netstat).
Here's my server code for good measure https://pastebin.com/1vq6EGRv

By default the server's host was bound to "::" so I figured I'd change that to 0.0.0.0 to suggest using ipv4. No difference. No errors being thrown, the ENet library would complain if initialization didn't succeed.
I'm completely out of ideas. Any tips would be greatly appreciated! Thanks

[Dancso]

Ok I figured it out. I lost multiple days troubleshooting this. Here's the "solution" for posterity:
Turns out, UDP requires data to be sent as it's not connection-based. I've been using online port checkers which may not even be trying for UDP, but it's certainly not sending any data. The test clients I've written for convenience, were also not sending anything.

Derp