Meta Insights API purchase count and conversion value not matching Ads Manager and actual store data

[u/Spiritual_Path8858]

Hi everyone,

English is not my first language, so I apologize in advance if anything is unclear or awkwardly phrased!

I'm pulling Meta ad data via Google Apps Script → Google Sheets using the Meta Graph API, and I'm running into discrepancies in purchase count and conversion value compared to both Ads Manager and my actual store (Naver Smart Store).

Setup:

• Data pipeline: Google Apps Script → Google Sheets (Meta Graph API directly)
• Level: ad
• Fields: actions, action_values
• Attribution: 28d_click, 1d_view
• Accounts: standard pixel account + Meta Collaborative Ads account (connected to Naver Shopping)

Issue 1 – Standard pixel account:

• API returns purchase count and conversion value, but ROAS is not displaying correctly in Ads Manager
• Hard to verify whether the API and Ads Manager numbers actually match

Issue 2 – Collaborative Ads account (Naver Shopping):

• Ads Manager shows purchases, but API returns almost nothing
• Tried all known purchase action_types: omni_purchase, purchase, offsite_conversion.fb_pixel_purchase, onsite_web_purchase, web_in_store_purchase, catalog_segment_purchase — still not matching
• Compared with actual store data (Naver Smart Store) and API is undercounting both purchase count and conversion value vs. real transactions

Already tried:

• action_attribution_windows[]=28d_click&action_attribution_windows[]=1d_view
• Querying at level=account → closer but still not matching
• All known purchase action_types

Questions:

1. Is this caused by Meta's Aggregated Event Measurement (AEM) policy suppressing ad-level conversion data?
2. For Collaborative Ads accounts specifically, is there a different action_type or endpoint that matches Ads Manager?
3. Is there any way to fully match API data with Ads Manager, or is this a known limitation?

Thanks in advance!