Long term, only paid ads and SEO will work (and SEO can be fickle)
Short term, run some paid experiments (knowing you will probably not get positive return yet) and maybe some influencer marketing (they'll cost money, but not as much as paid ads depending on the niche)
SEO is extremely easy: Write in very clear prose what you are selling and give potential clients as much information as possible. This is all you need for SEO, apart from purely technical stuff like load times.
Turning your SEO efforts into real sales is also easy: State your price(s) very clearly on the website and then make it as easy as possible for customers to make a purchase. Get out of their fucking way when they have their wallet out.
If you insist on using paid ads and influencers, by God connect the campaigns to specific discount offers so that you know exactly how many sales origin from each channel you are paying to market in.
Cannot be emphasised enough.
I have seen enough B2C funnel optimization work to be able to say that at every minor obstacle you create 90% of the people will fall off.
You need to get people invested in your solution and make it super easy for them to throw money at you.
So, usually paid experiments won't really give you a return at an early stage, but occasionally they can if you get lucky, but at least they'll give you an idea of what your CAC can be, and give you a starting point to start optimising it