If there is a problem with your API Key (I don’t know why there is a problem with my key) the response from the Responses API is:
I couldn’t find [question] in the provided files. Could you please provide more details or specify if you have another document or source where this information might be present?
Why it can’t just throw an exception or something I do not know. I spend hours debugging this only to eventually figure out one of my keys (that used to work) has stopped working for no reason that I know of. Create new key → code works again.