What should I A/B test first to reduce abandonment?

I've been running my Shopify store for two years now, and cart abandonment is killing me. We're spending good money on Meta ads, driving traffic that looks promising, but something breaks down at checkout. My conversion rate hovers around 2-3%, which means for every 100 visitors, only 2-3 actually purchase. I've tried generic discount pop-ups, but they feel spammy and don't really solve the core problem. I know visitors are interested—they're adding products to cart—but then they just... disappear. Is it the checkout process? Are my prices not competitive? Are customers getting cold feet at the last moment? I'm tracking everything in Google Analytics, and the data shows most abandonment happens between 'Add to Cart' and 'Complete Purchase'. This isn't just frustrating; it's directly impacting our monthly revenue. Every abandoned cart represents potential lost income, wasted ad spend, and missed growth opportunity. I need a systematic, data-driven approach to understand and reduce these drop-offs. Not just guesswork, but a strategic method to identify friction points and convert more of these hesitant shoppers.