1. Broken Pixel & Signal Loss
You see it as: Your dashboard reports 2 purchases, but Shopify shows 9. Your ROAS looks terrible even though revenue is there.
What's actually happening: Since iOS 14.5+, browser-based pixels miss ~30-40% of conversions. Without server-side Conversions API (CAPI), Meta's algorithm can't see who's buying — so it optimizes for the wrong people.
Check: Go to Events Manager → Data Sources → Is your Event Match Quality below 6.0?