How to Set Up Offline Conversion Tracking for ChatGPT Ads

Click identifier

oppref

Cookie

__oppref, 30 days

Browser identifier

__obref

API

OpenAI Conversions API

Endpoint

POST https://bzr.openai.com/v1/events

Auth

Bearer token

Event timing

Within the last 7 days

What you need before you start

Six things, and you can collect all of them before you touch a single setting. The two credentials both come from the same screen in ChatGPT Ads Manager.

The four moving parts

1. 1

   Capture

   The ad click puts an identifier in your landing page URL. You read it before the visitor navigates away, because it only exists on that first page.

2. 2

   Carry

   The identifier has to reach your form. A hidden field does this, filled in by a small script when the page loads.

3. 3

   Store

   The form submission puts the identifier into your CRM alongside the lead, where it waits for as long as your sales cycle takes.

4. 4

   Send

   When the deal closes, an automation posts an event to the platform API with the stored identifier, the outcome and its value.

Capture the oppref click ID

Get the identifier out of the URL and into a cookie that survives the rest of the visit.

<script>
(function () {
  var name = 'lt_oppref';
  var url = new URLSearchParams(window.location.search).get('oppref');

  // The URL only carries oppref on the landing page. On every later
  // pageview there is nothing to read, so do not overwrite what we stored.
  if (!url) return;

  var days = 30;
  var expires = new Date(Date.now() + days * 864e5).toUTCString();
  document.cookie =
    name + '=' + encodeURIComponent(url) +
    ';expires=' + expires +
    ';path=/;SameSite=Lax';
})();
</script>

Carry it into your form with a hidden field

Make the identifier part of the form submission, so it arrives wherever your leads arrive.

<input type="hidden" name="oppref" id="oppref" value="none">

<script>
(function () {
  var match = document.cookie.match(/(?:^|;\s*)lt_oppref=([^;]*)/);
  if (!match) return;

  var field = document.getElementById('oppref');
  if (field) field.value = decodeURIComponent(match[1]);
})();
</script>

Store it with the lead

Keep the identifier attached to the record your sales team actually updates.

oppref        The click identifier from the hidden field
click_date    When the lead came in, so you can spot stale ones
value         The deal value, filled in when it closes
currency      ISO code, e.g. EUR. Do not assume one currency forever

Send the conversion when the deal closes

Post one event to the OpenAI Conversions API with the stored identifier and the outcome.

{
  "events": [
    {
      "id": "deal-4821",
      "type": "lead_created",
      "timestamp_ms": 1773892800000,
      "oppref": "gAAAAAb123",
      "action_source": "offline",
      "data": {
        "type": "contents",
        "amount": 125000,
        "currency": "EUR"
      }
    }
  ]
}

curl -X POST "https://bzr.openai.com/v1/events?pid=<PIXEL-ID>" \
  -H "Authorization: Bearer <API-KEY>" \
  -H "Content-Type: application/json" \
  --data '{
    "validate_only": true,
    "events": [{
      "id": "test-1",
      "type": "lead_created",
      "timestamp_ms": 1773892800000,
      "oppref": "gAAAAAb123",
      "action_source": "offline",
      "data": { "type": "contents", "amount": 125000, "currency": "EUR" }
    }]
  }'

Confirm it is working, and keep confirming

Know that events arrive, and notice when they stop.

What breaks in production

Seven things that go wrong after the setup works. Most of them produce no error at all.

1. 1.The 7-day timestamp window

   OpenAI rejects events whose timestamp_ms is more than 7 days in the past. You cannot backdate a conversion to the moment of the click, which is what most people try first. Send the event when the deal closes, with the current time, and let oppref carry the attribution back to the original click.

2. 2.Sending the value in whole currency units

   The amount field is an integer in minor units. Send 1250 for a deal worth 1,250 euro and you have reported a conversion worth 12.50. Bidding then learns that your best leads are worthless. Multiply by 100 and round.

3. 3.One bad event failing a whole batch

   The API accepts up to 1,000 events per request, but a single invalid event fails the entire batch. If you send in batches, one deal with a missing currency takes the other 999 down with it. Send individually until your data is clean.

4. 4.Double counting with the OAIQ pixel

   If the pixel fires a conversion in the browser and your automation sends the same conversion server-side, ChatGPT Ads counts two. Send the same value as event_id on the pixel and as id on the API call, against the same Pixel ID, and it counts one.

5. 5.Consent blocking the capture

   If your consent banner blocks cookies until the visitor accepts, your script cannot store oppref and cannot fill the hidden field. Leads from visitors who decline will always show none. That is correct behaviour, not a bug, but it does mean your conversion volume is lower than your deal volume and you should know by how much.

6. 6.The form rebuild that drops the hidden field

   The most common way this breaks is a designer rebuilding the form. The hidden field is invisible, so nobody notices it missing. Add it to whatever checklist your team uses before a form goes live.

7. 7.Assuming the 30-day cookie limits your sales cycle

   It does not. The cookie only has to survive from the click to the form submission. Once oppref is in your CRM it stays there, so a deal that closes after four months still carries its identifier. What the cookie window does limit is a visitor who clicks the ad, leaves, and comes back to convert five weeks later.

What you maintain either way

If ChatGPT Ads is the only platform you run and your form never changes, the custom build will serve you well. The moment you want the same closed deal reported to four platforms with four different identifiers, the maintenance is the whole project.

The hard part of offline conversion tracking is not the API call. It is keeping a hidden field alive across three years of website changes and noticing when it stops working. Build the chain, then build the monthly check that tells you it is still connected.

Sources: OpenAI Conversions API reference · Conversion measurement