It can often be a bit problematic to sow lettuce and spinach in the middle of a heat period like now, as both germinate quite poorly when the soil temperature is above 20 °. You can try to sow in the evening, shade the seedbed, and give it all a regular sprinkling with cold water - and often you will still be badly disappointed when virtually nothing comes up.
The most effective way to get rid of such a late summer depression is to put the seeds in the fridge. The seeds are sprinkled between, for example, 2 moistened coffee filters, placed in a closed container (here an airtight cold cuts box) and placed at the top (or in the door) in the refrigerator where it is warmest. A 3-4 days where the seeds are exposed to both moisture (and thus absorb water) and a temperature around 5-8 ° is sufficient to break the seed dormancy, and you begin to be able to see the small white sprouts on the seeds. And then it can be sown as usual, whether it is as germination in a plug box or directly in the ground in a groove. Tweezers are recommended.