It looks like you got "Damping off" problem which mostly of fungal problem, but some bacteria can also caused that.
Growing Ficus from seeds for me is quite challenging. It requires moist but not too moist medium at first stage, since most fig's seed are so tiny. I try not to use perlite or large granules materials as it will made seed buried under them, also the base of seedling will be below the granules, this will cause too much humidity and reduce air flow at the base of the seedling stem, lead to rot by damping off fungal.
In my case for fig seeds, I used sterilized soil, just garden soil (we don't have much garden center at my place, I live at rural area, plus I have found garden soil is just fine for most of the time), I bake the soil in oven to kill all the germs, let it cooled, and sieved it into very fine particles. Water it just to moisture and put it in small container, tap it so that the surface is flat, you will need to compact the surface bit, loose surface will made seed buried into the medium (not good for figs). water it again once more, then while it is still moist, spread the seed. "Surface sowing" is needed, do not cover the seed with medium. then the seed pot can be sealed, untill the germination occurred, when the seedling appear, open the plastic sealing gradually to allow air in, too much humidity will cause damping off, too dry will also kill seedling, it is a tricky balance.
Another alternative is to use fungicide, there are many anti-damping off fungicide on the market, I'm not sure what available at your area, it can be used as preventive by spraying the surface of medium before seedling emerge or as treatment when the sign of damping off appear
Exposure to sunlight periodically could also protect seedling from damping off as the sun ray kills fungus and made seedling stronger, but it need to be done carefully as strong sunlight could also burn seedling (this technique is useful for anyone growing seed in tropics maybe, and when you don't have fungicide in hand)
I grow plants in tropics, so you might need adjustment accordingly to my suggestion
