Mold

Cut the rotten parts and spray with H2O2 - Hydrogen Peroxide to kill any mould spores. Be mindful that it might actually be catapillars that have gotten into the buds, if you see "web" like silk on the buds you can pull the bud apart and will see the @#£% catpillar making a home in the flowers... happens every year when I grow outdoors/green house

donìt listen to who suggest you to throw away the plant. If you spot bud rot , cut the bud and with a scissor eliminate the rotten part (every part!) . after that let it dry. the botrytis should stop. I did this often and never encountered problems. (it's advisable to cure the the buds in a different jar with a humidifier sensor inside.)

Foliar spray is a great idea for immediately providing a specific mineral that is capable of transitioning the stomata to an area of need - i.e. existing problem / symptoms etc. foliar spray for other reasons is mostly masturbation. preventative sprays are useful. context-specific reason i'm too unimaginative to think off off the top of my head is also a good reason. doing it just to do it is stupid. roots are more than capable of providing everything. when they are not the first thought should be to correcting the formular not a bandaid action like applying some mineral locally to a leaf. unnecessary foliar sprays do not follow the "keep it simple, stupid" mantra. So, don't be afraid to use them for a good reason. Spraying flower is even more restrictive, though. btw, when you can see it, that means it's been there longer and already spreading. obviously the sooner you catch it and remove it the better off you are. inspect daily for new visible infections.

Outdoor grow? Happens to me every year as I live in a very wet climate. I know people say to chuck the whole thing. I never do. I cut out the moldy parts, water well, add some fresh compost, and let her get on with it. The spray might play a part here. Check airflow, too. Wet buds need air to dry! Cut leaves, stems, whatever is restricting airflow around flowers.

Throw away the plant. Make sure to clean yourself and change clothes.. go back and clean the room with bleach or alternative cleaning solutions. If you have other plants go over them, making sure not to transfer spores from the infected plant onto them if not done already. If it has already. Then toss them as well. Take this as a learning experience although it hurts.. you learned. Next time keep RH% 45-55% in bloom, and do not spray them in flower! Keep good air flow going, to remove excess moisture off the buds. Good airflow, low humidity and a even canopy are the keys to success in flowering stage! Sorry for the loss man. I know it sucks 😕

Oh yeah I'm with the others that replied on this. Get rid ASAP. I never spray when in flower due to the chance of this happening. If your 100% certain it's because you sprayed the plants then don't do it again. If your not 100% certain this caused it then check your environment conditions. This stage they prefer lower Rh, if your rh is 60% or above then that could have been the reason for this. Don't pick my answer as I don't compete in Gotm.

Burn everything! And above all, thoroughly disinfect the growing area before putting other plants back in.

Throw it away. Mold has spores and they are not good for your health. I never use foliar sprays for this exact reason.

What is your environment like, temp and rh%? You sprayed it one time? How long ago?