Error: Could not create the Java Virtual MachineError: A fatal exception has occurred. Program will exit.
Invalid maximum heap size: -Xmx12288mThe specified size exceeds the maximum representable size.
Edit - Yes, I know this is my first post, and that I joined today. I made an account just to post this because I can't play the modpack.
Try allocating more ram or installing a newer version of java.
It does say that the maximum heap size is over it's limits, did you allocate ram through the twitch launcher? Or did you do it by hand? If you did it by hand, try using the Twitch launcher.
Proud creator of Ultimate Compression: https://minecraft.curseforge.com/projects/ultimate-compression?gameCategorySlug=mc-mods&projectID=304462