---
title: Facebook Conversions API Diagnostic Guide
slug: facebook-conversions-api-diagnostic-guide
docTags: 
createdAt: 2025-08-01T19:38:45.236Z
---

If you're experiencing issues with your Facebook Conversions API (CAPI) destination, this guide will walk you through common problems and how to resolve them. Each flow below addresses a specific issue with step-by-step troubleshooting instructions.

## Events not appearing in events manager

**Symptoms:**

- Expected server events (like `Purchase`) are not visible in Meta Events Manager.
- You’ve recently configured CAPI but see no activity.

**How to troubleshoot:**

1. Confirm the CAPI destination is created in Chord CDP and has an active connection with a back end source. 
   1. Verify the Pixel ID and Access Token values for the destination correspond with the values listed in your Meta Business/Events Manager account
2. Go to Meta’s **Test Events tool** and trigger a known action.
3. Look for **HTTP 200 responses** and verify no errors like: 
   - `401 Unauthorized` → Invalid token or app config
   - `400 Bad Request `→ Missing or incomplete payload
4. Retry with a minimal payload (just `event_name`, `event_time`, and `user_data`) to isolate the issue.

## Duplicate events or overcounting

**Symptoms:**

- Conversion counts appear inflated in Meta Ads Manager.
- Same action appears twice under “Received Events.”

**How to troubleshoot:**

1. Check whether **Pixel and CAPI are both firing** the same event.
2. Confirm the `event_id` field is included in both and matches exactly.
3. Visit Meta Events Manager → **Diagnostics tab** to see any deduplication warnings.
4. Use the **Test Events tool** and look for a single deduplicated instance of the event.

## Low match rate or inaccurate attribution

**Symptoms:**

- Meta Ads Manager reports poor attribution for key campaigns.
- Low conversion match rates despite CAPI being enabled.

**How to troubleshoot:**

1. Confirm that `user_data `includes identifiers like: 
   - `fbc `/ `fbp`
   - Array of hashed external\_ids including Anonymous ID and User ID
   - Hashed email (`em`)
   - Hashed Phone (`ph`)
   - Hashed zip code (`zp`)
   - Hashed country (`ct`)
   - Hashed first name (`fn`)
   - Hashed last name (`ln`)
2. Turn on **Advanced Matching** in the Meta Pixel settings.
3. Optionally, A/B test campaigns with vs. without CAPI enabled to evaluate impact.

## Best practices recap

| **Recommendation**       | **Why It Helps**                      |
| ------------------------ | ------------------------------------- |
| Use CAPI + Pixel         | Covers blind spots, improves accuracy |
| Use matching `event_id`  | Prevents overcounting                 |
| Include full `user_data` | Boosts attribution match rates        |
| Monitor Diagnostics tab  | Flags misconfigurations               |
| Test frequently          | Verifies end-to-end setup             |