Failing (not set) on Server Events sent by Stripe

[fab_009x]

Hi Stape Community,

I’m facing a persistent session stitching issue with GA4 server-side events and would love to get some insights from you.

Our Architecture & Pipeline:

1. Trigger: A user signs up for a trial on our web app. Stripe generates a subscription/trial event for 7 days. After 7 days Stripe makes the payment and sGTM triggers the purchase event.

2. Backend: Stripe fires a webhook to our custom Node.js backend.

3. sGTM Forwarding: Our backend extracts the active browser cookies (_ga and _ga_CONTAINER_ID) at signup time, enriches the payload, and POSTs it to our sGTM container hosted on Stape.

4. Destinations: sGTM processes the event and dispatches it to GA4, Meta CAPI, and Google Ads.

The Issue:

Client-side web events (page_view, etc.) are tracked and attributed properly in GA4.

However, our server-side start_trial, purchase event sconsistently ends up under (not set) for Session Source / Medium in GA4, despite passing both client_id and a fresh, live session_id in the webhook payload.

Webhook Payload Structure (Sent to sGTM):

JSON

{
  "client_id": "1981365705.1786007408",
  "event_name": "Data",
  "user_id": "cus_V1QAKJV24D75q3",
  "ip_override": "4.233.222.216",
  "user_agent": "Mozilla/5.0 (Windows NT 10.0; Win64; x64)...",
  "timestamp": 1786007498,
  "events": [
    {
      "name": "start_trial",
      "params": {
        "currency": "EUR",
        "value": 0,
        "session_id": "1786007406",
        "em": "82314bd6e57...",
        "ph": "99e25c9d822...",
        "items": [...]
      }
    }
  ]
}

What We Have Already Verified & Configured:

• Timestamp Freshness: We verified that session_id (1786007406) is parsed live from the active _ga_CONTAINER_ID cookie and matches the web session start time within 90 seconds of the webhook execution.

• Key Path Mapping: In sGTM, our Event Data variable {{EDV - session_id}} uses the key path events.0.params.session_id.

• Tag Parameter Overrides: In the GA4 Server Tag, we explicitly map session_id = {{EDV - session_id}}.

• Client ID: client_id is passed at the root level of the JSON payload.

Our Questions for the Community:

1. Is there any specific parameter required by GA4 Server Tags (e.g., engagement_time_msec, session_number, or _s) to successfully force session stitching for offline/server webhooks?

2. Could there be an issue with how the Client / GA4 Server Tag handles the session_id parameter when nested inside an events array?

Any suggestions or troubleshooting ideas would be greatly appreciated!

[Roman_Kaliniichuk]

Hi,
Most likely, you’re currently facing the following situation: when you view the report for a specific user’s session, the event is associated with that session, but the event itself is displayed under “(not set).”

To properly attribute an offline event, you need to pass the following parameters: session_id, session_number, client_id, engagement_time_msec, and the user’s IP address.

If these parameters are passed and matched correctly, the event should be attributed to the corresponding session.

In some cases, we also recommend passing UTM parameters. However, keep in mind that doing so can effectively override GA4’s traffic source attribution. I’d recommend testing it without the UTM parameters first, while making sure that all the parameters listed above are included.