I can't make sense of "subscription missing proper authorization"

You are creating an application to allow you to get permission to read a streamers subscriber data.

Not quite sure what you mean “outside of Twitch” you do need to use the Twitch Dev Console to get a ClientID to use.

So to read ninja’s subscribers vai the channel:subscribe topic.

  • You create an application/clientID
  • Then you create a website to handle the oAuth flow steps
  • Then you ask ninja to authenticate/grant access between their Twitch account and your application
  • Then you can then generate a Client Credentials token to create an EventSub Subscription on the channel:subscribe topic that’ll send data to your AWS endpoint(s)