I would suggest you to stop the conversion campaign for a while, focus on traffic for now.

As for Retargeting, in my opinion don’t create a lookalike audience, instead use people who actually visited the website in last 30 days or initiated checkouts, added to cart, or spend some time on your site. Now, this is just the backend part, for frontend you need to create good graphics, better than before and plant an offer in the ad to lure customers. Use friendly ad copies which offer a solution to the potential customers.

For Traffic – Brainstorm with your friend, who will be your ideal customers and check out the data from the purchases to get the demographics of your existing customers. Combine them and add possible interests and try that audience. Have 3 separate ads with completely different audiences and see what’s getting the best results and invest more. You can start with the lowest amount possible.

You can also try to upsell existing customers, create a separate ad for them, include some offers and see what happens.

If lookalike is not working for you, stay away from it for another 3 months. Give Facebook more data to understand your audience and then you can try it again.