AI writing plugin says my openai key is invalid even though it's brand new

If billing is sorted and it still fails, test the key outside the plugin. One curl request to the models endpoint tells you in seconds whether the key works. If it does, it's the plugin. Also check the key's permissions in the dashboard. Keys can be limited to a project or set to restricted access, and a restricted one gets rejected on the calls the plugin actually makes.

Yes, the API needs its own billing with credit on it, it's separate from a ChatGPT subscription. Without it a key usually fails with a quota error, but some plugins just report that as invalid. The other common one: newer keys start with sk-proj- and are longer than the old format. Some older plugins check the key format before even trying it and reject anything that looks different. Update the plugin, and check you didn't paste a trailing space.