You're getting clicks, so your ad itself is doing its job, the issue is likely after the click. There may be reasons such as the audience not being precisely targeted, the landing page being irrelevant, the call to action being unclear, or the users who are coming after clicking the ad having difficulty navigating the site or completing the purchase. Improving targeting, increasing page relevance, making a highly relevant CTA, and reducing the complexity of the conversion process will help improve the conversion rate.