Depends how you code your extension and backend.
Pubsub technically no
EBS yes.
You don’t have to use pubsub to communicate.
However,
EBS no in theory. You could go completely serverless, but that would mean exposing your extension secret to the world.
But
The EBS is a scenario such as yours, reads in a POST request from the config panel, verifies it and checks the channel about to send to is the right channel for the sending message and then creates a pubsub message, using your extension secret to compose the security component.
A serverless one would likely be rejected due to the exposure of the secrets.
https://github.com/twitchdev/extensions-samples/tree/master/boilerplate here is the boilerplate
The Extension PubSub docs describe how to send messages. It’s a system that you don’t have to use at all. It’s just there if you want it.
All of my code on my public extension deals with relaying a pubsub message from some source, so theres nothing to share aside from a working POST request… Which matches the documentation.
All of the other code is display logic for my messages I send over pubsub.