Check the funnel in order: CPM (cost of reach), click-through rate (creative), landing page to add-to-cart rate (product page), cart to checkout and checkout to purchase (site and checkout). Whichever step changed most is the cause. If CPM and CTR are stable but cart to checkout falls, the problem is on your website, not in Meta.
Step 1: compare two equal periods
Pull last 7 days against the 7 days before for CPM, CTR, CPC, landing page views, adds to cart, checkouts started and purchases.
Step 2: find the step that moved
| What changed | Likely cause | Fix |
|---|---|---|
| CPM up | Seasonal competition (Q4), narrow audience, low-quality ads | Broaden audience, refresh creative, accept some seasonality |
| CTR down | Creative fatigue | New hooks, new angles |
| Add-to-cart rate down | Product page, price, stock, offer | Check page, reviews, variants in stock |
| Cart to checkout down | Cart drawer, shipping surprise, site bug | Test cart on mobile, check console errors |
| Checkout to purchase down | Payment options, trust, costs at checkout | Check express pay, shipping rates |
Step 3: check what you changed
New apps, theme updates, price changes, discount codes ending, budget jumps over 20%, and edits that reset learning all show up as sudden CPA changes.
Step 4: check tracking
If Shopify orders are steady but Meta purchases dropped, tracking may be broken rather than performance. Compare the two before acting.
Don't panic-edit
Multiple changes at once make it impossible to know what fixed it. Change one thing, wait 48 to 72 hours, then review.
Growth bottleneck audit
Frequently asked questions
Why is my CPA high but my CTR is good?
If people click but don't buy, look at the landing page, price, shipping costs and checkout. The ad is doing its job; the site isn't converting.
Do CPMs rise in Q4?
Yes. Competition increases from October through Black Friday and Christmas, so CPMs typically rise. Offers and stronger creative help offset it.
Should I pause campaigns when CPA spikes?
Not immediately. Diagnose first. Pausing resets learning and can make performance worse when you restart.
Written by Shimeez Bok, founder of Growth Alchemy, an ecommerce growth studio in Auckland, New Zealand.
