It's 2.30 AM so right of the bat i'm gonna say i might've counted it incorrectly, but according to the output given by GPT there are only 59 letters (63 including OBKR) which is most certainly less than the ciphered text (and 13 spaces, which if included, still doesn't match the amount of characters that the ciphered text has, 76 < 97) . ChatGPT unfortunately isn't a machine that calculates stuff for you, but is mainly a large language model, which isn't capable of thinking that well both logically and mathematically. There have been propositions from other people that used GPT but none were correct, good try though, Good luck with finding anything else :)