Grab the cinnamon and sprinkle it on the soil.

How much are you watering? Maybe too much? Seeds under a dome don't need watering at all. When I plant seeds I wet my soilless mix so it is wet right through but I'm careful not to over wet it. As I'm mixing in the water I grab handfuls and squeeze. Some water should come out but not a lot. Then I fill my containers and plant my seeds and put them under the covers. I do not water them again while sprouting and most times not for a while after I remove the covers.

EG I started my snaps. Put on the covers and put them on the heating mat and under the lights. It took almost a week for them to germinate. I moved them off the mat and took off the covers and put them back under the lights. It took another week before they were dry enough to water. Remember you are inside and there is no sun or wind to dry out your plants and if you have normal humidity in your house the only way moisture is removed is from evaporation

Hmmm, then I guess I overkill with kindness ;)
Thanks for your input!

I always try to water from below the container and not above. Also you could add a layer of sand after you've sown the seeds so fungus will not contaminate the soil. Also it's a good thing to have a fan circulate air indoors. Helps to dry up moisture from the leaves.

I use Fertiloam brand to start my seeds, I highly recommend it. I also keep an oscillating fan on 24/7. Dowlingram gave great advice :-) I've never had any luck with cinnamon or chamomile tea, only keeping the fan on helped. It also makes the plants sturdier and more ready for outside conditions.

Water with chamomile tea, which has anti fungal properties.
Put a fan near the seedlings and keep it on for several hours each day. Air movement and good circulation will help prevent any problems.
When you pick up and handle the pots or trays or seedlings, give them a good shake to help toughen their stems.