Sow 2-3 basil seeds per cell or pot, planting them 1/4″ deep and firming the soil well over top.
Keep the trays or pots warm (between 75°F and 85°F) and moist until germination—which should happen in about 5-7 days in ideal conditions. You can help maintain these conditions by using a humidity dome or by covering your trays with plastic wrap, removing once the seeds have germinated.

I suspect they are drying out. I usually grow mine from seed. Follow Owds advice.
2 yrs ago my youngest girl bought basil in a pot from the fresh herbs section at the local supermarket and she split them up to ended up with over 10 pots of plants.

Thanks both, I guess I did wrong - I scattered a whole packet of seeds in a large tray in my greenhouse where it’s warm, and watered them every day. Maybe something will come up.

That's a shame, Hank ... maybe they were just too wet? It's so easy to give them too much care!