Nvm. String needs to be a hex string. Your documentation seems to be outdated.
Discussion
yes. you sign a hash.
where is it wrong?
https://guides.getalby.com/developer-guide/v/alby-browser-extension-apis/window.nostr/signschnorr
The code example says
const signature = await window.nostr.signSchnorr("some text here");
But that would throw