Two sources: Meta-reported (pixel+CAPI) vs Postback (S2S). Often disagree 5-20%. Meta for bidding signals; postback for business reporting.

Postback vs Meta conversions — which to trust

Two attribution sources: platform-reported conversions (e.g. Meta pixel + CAPI, Meta's algorithm) vs Postback-reported conversions (server-to-server from tracker, no browser dependency). In Wevion's Ads Manager there is one conversion column with a switchable source (not two side-by-side columns), and the default source is postback (verified conversion-source-store.ts). Selectable sources: postback, all, meta, google, taboola, tiktok, snapchat, outbrain. Platform vs postback counts often disagree by 5-20%: platforms tend to over-attribute; postback is closer to actual. Switch the source per use case (postback for business truth; a platform source to match that platform's bidding view).

Who is this for

Affiliate marketers + e-commerce mediabuyers running tracker-based funnels. Anyone whose Wevion Ads Manager shows N conversions while postback dashboard shows M conversions for the same campaign.

The two attribution sources

Source 1: Meta-reported conversions

How Meta tracks:

• Browser pixel fires on conversion event
• Plus CAPI (server-side) fires same event
• Meta's algorithm attributes the conversion to an ad based on attribution window (7-day click + 1-day view default)
• Deduplicates pixel + CAPI via event_id
• Reports back to advertiser

Visible in: Meta Ads Manager + Wevion's per-platform Meta column.

Source 2: Postback-reported conversions

How postback tracks:

• Tracker server logs conversion (Keitaro, Voluum, etc.)
• Fires HTTP POST to Wevion's postback URL with click_id
• Wevion matches click_id → ad campaign attribution
• Counts as conversion attributed to that ad

Visible in: Wevion's postback dashboard + per-campaign postback column.

See com-109 postback overview.

Why they disagree

Net result: Meta often over-attributes by 5-20%. Postback is closer to actually happened.

When to trust which

Trust Meta for: bidding + optimization

Meta's algorithm makes bidding decisions based on its own attribution. If you tell Meta "optimize for purchases" + Meta sees 100 purchases, it optimizes based on those 100.

If you only feed Meta postback-reported (say 70 purchases), Meta optimizes based on 70 — and may under-perform because it has less data.

So: use Meta's CAPI / pixel data for optimization signals. Don't try to reconcile Meta's bidding-side view with postback.

Trust postback for: business reporting + reconciliation

For "did we actually make money?": postback is closer to truth.

• Revenue calculation: postback total
• Profit calculation: postback total minus costs
• Client reporting: postback (defensible / auditable)
• LTV analysis: postback (matches actual buyers)

Document the discrepancy

Don't pretend they agree. Document for each campaign:

• Meta-reported conversions: X
• Postback-reported conversions: Y
• Discrepancy: Z%

If discrepancy > 25%: investigate (something likely wrong with one source).

Reconciliation workflow

Monthly reconciliation:

1. Pull Wevion's Meta-reported total
2. Pull Wevion's postback-reported total
3. Calculate discrepancy
4. Look for patterns: certain campaigns / dates / placements with bigger gaps?
5. Document acceptable threshold (10-20% typical)
6. If beyond threshold: investigate (pixel issue, postback issue, click_id flow)

Choosing the conversion source

The conversion column has a single switchable source selector (persisted per user):

• Default source: postback
• Other sources: all, meta, google, taboola, tiktok, snapchat, outbrain
• The column shows the count for whichever source is selected — there is no side-by-side dual column and no built-in discrepancy indicator in the table

To compare platform-reported vs postback, switch the source back and forth (or reconcile via exports).

For exports / client reports: pick a source consistently (don't mix).

Wevion's role in reconciliation

Wevion does NOT decide which source is "right". Wevion presents both + tracks the discrepancy.

You make the call per use case.

For affiliate marketers: postback often primary source (Meta data less critical when most traffic isn't directly attributed to Meta).

For direct e-commerce: Meta primary (pixel/CAPI reliable for own-site conversions).

Common patterns by business model

Direct e-commerce (Shopify / WooCommerce)

• Primary source: Meta pixel + CAPI
• Secondary: own analytics (GA4, Shopify Order Attribution)
• Postback: optional if you also use a tracker

Affiliate marketing (Keitaro funnels)

• Primary source: postback (truer to actual)
• Secondary: tracker's own attribution
• Meta-reported: for optimization signals only, not business truth

Mixed (own site + affiliate)

• Two streams of data:
  • Direct: Meta CAPI primary
  • Affiliate: postback primary
• Separate reports per stream
• Don't blend; clarity matters

Disagreement size as signal

• 0-5%: noise; ignore
• 5-15%: normal; both functioning
• 15-30%: investigate (pixel or postback issue)
• > 30%: likely a setup problem (pixel broken, postback misconfigured, attribution model mismatch)

What you'll see in Wevion

In the Ads Manager table:

• A single conversions column whose value reflects the selected source
• A source selector (default postback; also all, meta, google, taboola, tiktok, snapchat, outbrain)
• No side-by-side dual column and no automatic discrepancy % in the table — switch the source to compare

Common questions

• "My Meta says 100 conversions, postback says 75. Which is right?": both, for different purposes. Real conversions probably closer to 75 (postback). Meta sees 100 because of view-through + cross-device.
• "Should I disable Meta CAPI and just use postback?": NO. Meta needs CAPI for bidding optimization. Use both.
• "My discrepancy is 50% — what's wrong?": investigate. Likely: click_id not flowing through to tracker, or pixel only firing on certain conversion paths.
• "Can I get one unified number?": no — they're fundamentally different attribution methods. Pick one consistently per use case.

Best practices

Pick primary source per business case

Don't switch mid-month. Pick + document + stick with it.

Run both for redundancy

Even if you primarily trust one: run both. Lets you detect issues with either source (if one drops to 0, you know something broke).

Educate stakeholders

Clients / executives often confused by discrepancy. Explain: Meta's view = what Meta credits itself with; postback view = what your tracker confirms. Use the right one for the conversation.

Reconcile quarterly minimum

Periodic check prevents drift. If Meta + postback drift apart over time: investigate.

Steps

1. Pull Wevion's Meta-reported total
2. Pull Wevion's postback-reported total
3. Calculate discrepancy
4. Look for patterns: certain campaigns / dates / placements with bigger gaps?
5. Document acceptable threshold (10-20% typical)
6. If beyond threshold: investigate (pixel issue, postback issue, click_id flow)

Last updated: 2026-05-17

Related articles

• Campaign metrics explained
• Postback (S2S) tracking overview
• Postback vs pixel — which to use