When ChatGPT was new (late 2022 through most of 2024) it often made up citations that didn't exist. That's because it didn't have the ability to search the web, and it was designed only for generating plausible sounding text. It wasn't designed to look things up.
Now that ChatGPT and all the major models can search the web, this is less of a problem.
However, it can still happen that a citation isn't correct. That's because the search engine attached to the AI may not be up to date, or it may be blocked by certain sites, or it may summarize incorrectly.
So for your academic work, it's still better to use Library Search, Google Scholar, or databases for your discipline instead.