transparent layer becoming a solid black on download

what it says in the title, when i've finished making sprites on a spritesheet with no background and download it it puts a solid black backing on it, i can't figure out the Contiguous fix i see everywhere online as i can't find the option to pick a color for transparency, i NEED to fix this, i am unable to sleep, it is 1:30AM and i having to get up in the morning to do this, please help me.