Brown/Black Taproots. Noob needs help

Hello everyone,

I'm new to this, so I'm trying to figure out what went wrong so I can get it right the third time.
I'm using a 600w LED Viparspectra in a small, empty bedroom with mylar sheets taped around.
My temp stays at around 75F - 80F and my humidity 35-40% and I also have a couple fans running to blow fresh air in.

For the grow, I germinated 2 cheeseberry seeds from 00 seeds/Bonza using the papertowel method in a ziploc and let the taproots grow for 24 hours until I saw the first sign of their taproots, then I put them into rinsed coco coir + perlite with no extra watering. About 1/4" deep. They looked fine before going in

That was on 5/1. I put them straight under the light at about 20", which I was told by a more experienced grower is the right height. After a couple days, the soil was mostly dry (to my 2nd knuckle) so I gave them another 1/2 cup of water each. Since it's been 4 days and I saw no sprouting, I got suspicious and brushed them up and what do you know--they're black and brown.

I'm certain they're dead, so I'm germinating another single seed to try again now, but I want to know what am I doing wrong and what could have caused this?

I'm also wondering could it be my coco coir causing this? Because I tried a grow before this one too (same seeds, same set-up) and I had damping off after week one, so this time I made sure not to overwater. But in any case I added photos of the other grow too.

When they are germinating in the soil you need to keep the soil moist, you should only plant them about a 1/4 inch in soil/coco.. then keep it moist. Looks like they dried up to me also i would skip the paper towel method and just put the seed in the soil and let it grow. i have read that with using a paper towel that the little tap root you see actually has small (not visible by eye) roots growing into the towel. so when you pick the seed up it breaks the small roots, but it has worked well for a lot of people for a long time. But just planting the seed straight in your medium takes away all risk. Good luck

Also the damping off problem will probably happen again, it is a disease that can stay on tools in soil etc. here is a link so you can read some on it. https://www.extension.umn.edu/garden/yard-garden/diseases/damping-off/