Not enough water. Did you water soil to runoff before placing seed? Are you spraying them or the soil? Can spray seedling soil and domes. Don’t spray them directly.
They look dry to me. Can you put a dome over them? A clear plastic cup or water bottle? Spritz some water inside the dome and place over the plant. Also give some water to the medium in a circle around the plant but a 1/2”-1” from the stem.
I mist the inside of the dome twice a day (after media is damp) using distilled water. The action of removing dome to mist it is enough air exchange at this time.