GM_addStyle is not defined (or another GM_ function)
What you see
ReferenceError: GM_addStyle is not defined
Why it happens
GM_ functions only exist when the script’s header asks for them with @grant. ChatGPT often writes @grant none and then uses GM_addStyle or GM_xmlhttpRequest anyway.
The fix
- rightsocket does this Adds a @grant line for every GM_ function the script uses, and @connect for sites it fetches.