I am on 18.2 beta and cannot get ChatGPT to work. Even the sample query "Ask ChatGPT to write a poem" suggested on the ChatGPT Integration & Privacy screen results in an error message that reads "Sorry, I don't understand."
I have ChatGPT turned on and Confirm ChatGPT Requests turned off.
I figured out the fix for this… at the time of setting up ChatGPT by turning it on and logging onto my premium account, there was a ChatGPT app update pending.
As a workaround, force update ChatGPT, go back to settings, toggle ChatGPT off in Apple Intelligence, turn it back on, re-sign in, and presto!
The best I can guess is that the API messes up when attempting to log in when not using the latest available version of the app.
It's still an issue Apple needs to fix as this wouldn't be apparent to end users, but I can verify the workaround fixed it for me in iOS 18.2 beta 1.