When someone buys from you, Meta should hear about it two ways: through the browser pixel (in their browser) and through the Conversions API (from your server). Right now, the server-side path is only sending 38% of what the browser sees.
For a skincare brand, iOS users are usually your highest-value buyers — and they're the ones Apple privacy blocks hardest. Meta is optimizing your bids based on roughly half your actual purchase data. The fix is a Shopify integration that takes about 90 minutes. After 14 days, expect reported ROAS to climb 5-15%.