Are you covering them after you sow? They require darkness to germinate, and then when they start to grow, light. I use a black bin bag.

They self seed, esp in gravel and the gaps in paving. Moist well draining soil and heat is all they need.

Obviously, read the sowing instructions carefully, always use a proper seed compost, (fine and low in nutrients) but as seeds have become more expensive, I would urge you to buy yourself an electric propagator. It will be one of the best investments you have ever made.

What procedure have you followed when trying to grow them? They're pretty easy really, usually, they need a temperature between 15-18 deg C to germinate, free draining mix to grow in. You haven't said whether they just don't germinate or whether they do, but something happens to the seedlings...