Starting with no audience when using Facebook ads can be tricky as it’s very easy to waste budget quickly targeting the wrong people. If you have not already, create a customer profile to use as your inspiration when building the targeting settings for your audience.
If you’re selling to a ‘cold’ audience who have never heard of your product before, consider the ad messaging you are using. You might need to educate people about your brand before you can sell to them. Then once people have engaged you can send them remarketing ads.
It’s also important to understand what you are willing to spend per conversion. A lot of o people say that Facebook ads do not work when they have not been realistic which how much they need to or are willing to spend to generate the conversion.

Hope this helps ?
David.