Getting "incorrect user authorization" error from Helix API

[BarryCarlyon]

You have used a client_credentials token
This token represents an application, not a user.

You need to get a user token from the broadcaster_id you want to update the channel information of.

See user Access Tokens: Authentication | Twitch Developers
And Reference | Twitch Developers

@rrgwllsl

So far as I understand that is the correct type of OAuth token for changing a stream title.

It is not no

@rrgwllsl

For the sake of debugging I also tried creating a token using Twitch OAuth Token Generator but it gave me the same HTTP 401 error (which is what should happen, so far as I know).

Sounds like you got a token for YOURSELF, but not for the channel you are trying to update.