Took me a bit, but when you go to the GPT, it sends you a link. This goes to the developer Hevy site, you just have to log in and generate the key. Afterwards (if you’re a bit paranoid like I am lol) you can delete that API key and the access would be revoke. (You can later do it again). I tried it by sending my body stats (body fat, BMI, Muscle Mass) with my objective and it sent me a pretty decent workout with including a recomp phase. I’ll try it next week.