Reddit Ads Adds Referrer URL and Order ID to Post Conversion Events

On September 8, 2026, Reddit Ads expanded the Conversions API by adding two fields to the Post Conversion Events operation: referrer_url and metadata.order_id. The first parameter allows advertisers to pass the URL of the page from which a user arrived at the conversion page. The second stores the advertiser’s internal order identifier.

The update is primarily important for online stores, analytics platform developers, and agencies that use server-side event transmission. It does not change advertising formats, bidding algorithms, or the attribution model. Instead, it expands the structure of conversion events.

What Is Reddit Post Conversion Events?

Post Conversion Events is a Reddit Ads API operation for sending data about users’ actions on a website or another supported source. It is used in the Reddit Conversions API (CAPI), a tool for server-side conversion tracking.

Unlike the Reddit Pixel, which runs in the browser, CAPI sends events from the advertiser’s server. For example, after an online store processes a payment, it can send a Purchase event to Reddit.

The operation is POST /api/v3/pixels/{pixel_id}/conversion_events. The request specifies the event type, time, source, identifiers used for matching, and additional parameters. Supported events include Page Visit, View Content, Search, Add to Cart, Purchase, Lead, and Sign Up, as well as custom events.

How Event Transmission Worked Before

Before the update, Reddit already accepted event types and timestamps, user information, purchase value and currency, products, and a unique conversion identifier.

However, there was no separately documented referrer_url field for the page immediately preceding the conversion. Advertisers could send event_source_url, meaning the URL of the page where the event occurred. These are two different types of data.

In addition, the API did not provide a separate metadata.order_id field for the order number from an e-commerce system. It had conversion_id, intended to identify and deduplicate a conversion event, but a technical event ID does not always match the business identifier of a transaction.

What Changed on September 8, 2026?

Reddit added two optional fields.

referrer_url contains the URL of the page that directed the user to the conversion page.

metadata.order_id contains the order identifier assigned by the advertiser.

For example, a user opens a product page and then proceeds to checkout. In that case, event_source_url may point to https://shop.example.com/checkout, while referrer_url points to https://shop.example.com/products/office-chair.

Referrer URL provides additional context about the user journey and is useful for event diagnostics. However, it does not prove that the specified page generated the advertising conversion. Reddit attribution is determined by other mechanisms, including matching the event to ad interactions.

In some server-side applications, the referrer_url value must be captured and stored separately: a server does not always automatically know the address of the preceding page.

Order ID vs. Conversion ID: An Important Distinction

The metadata.order_id parameter lets advertisers send an internal order number, such as ORD-2026-45821. Reddit accepts a string identifier of up to 100 characters; longer values are truncated.

Order ID helps connect an event to an order in an online store, CRM, or database. But it should not be confused with conversion_id.

conversion_id identifies the conversion event and plays a role in deduplication. An order and an event are not always the same object. For example, a single order may involve different events, while several systems may report the same purchase.

Sending the same order_id again does not mean Reddit will automatically eliminate duplicates. When Pixel and CAPI are used together, advertisers must follow the deduplication rules that use conversion_id.

How to Send the New Parameters

There is no need to create a new API method. Advertisers continue to use Post Conversion Events and add the necessary fields to the request body.

A simplified purchase example:

{
  "data": {
    "events": [
      {
        "event_at": 1790000000000,
        "action_source": "WEBSITE",
        "event_source_url": "https://shop.example.com/checkout",
        "referrer_url": "https://shop.example.com/products/office-chair",
        "type": {"tracking_type": "PURCHASE"},
        "metadata": {
          "conversion_id": "purchase-event-45821",
          "order_id": "ORD-2026-45821",
          "currency": "USD",
          "value": 150.00
        }
      }
    ]
  }
}

This is a schematic example of the structure, not a ready-to-use integration. Actual requests must meet Reddit’s requirements for authorization, matching identifiers, Pixel ID, and other fields.

In this example, event_source_url identifies the event page, referrer_url identifies the preceding page, and order_id stores the order number separately from the technical conversion identifier.

Why the Update Matters for Online Stores

A large store may use a website, a payment gateway, a CRM, and its own analytics system at the same time. A single order appears in multiple systems under a shared identifier.

That identifier can now also be included in a Reddit CAPI event. This helps diagnose purchase event transmission and identify errors in a server-side integration.

For example, if a payment service resends a payment notification, a developer can compare internal records and check whether the system created a second conversion event. However, preventing duplicates must still rely on Reddit’s designated mechanism, rather than merely including order_id.

Referrer URL may also help identify which section of a website the user came from before checkout. But Reddit has not claimed that providing this field, by itself, increases ROAS.

What Changes for Agencies and Analytics Platforms?

For agencies using ready-made Reddit Pixel or Conversions API integrations, the September update may be barely noticeable in the Ads Manager interface.

For developers of proprietary reporting systems, it provides additional ways to validate events. When auditing an integration, it is useful to check whether event_source_url is passed correctly, whether referrer_url reflects the actual preceding step, whether order_id matches the order number in the e-commerce system, and whether duplicates are created when events are sent from multiple sources.

It is important to distinguish technical diagnostics from ad attribution. Additional fields do not guarantee that Reddit will match every transaction to an impression or click. That requires valid user identifiers and other signals.

Post Conversion Events Limitations

Reddit recommends sending events as close as possible to the time they occur. Events must be submitted no later than seven days after the conversion.

When Reddit Pixel and CAPI run in parallel, proper deduplication is necessary. Sending identical orders without a consistent conversion_id can distort reporting.

The integration must also account for API limits on request volume and transmission frequency. Personal data must not be sent in URLs without complying with applicable privacy requirements. Particular attention should be paid to URLs containing sensitive query parameters.

Does the Update Affect Reddit Ads Performance?

As of October 2026, there are no independent studies confirming a measurable increase in conversions or ROAS directly resulting from the addition of referrer_url and order_id.

The update expands event data but does not introduce a new type of optimization. A more complete integration may indirectly improve analytics quality, but that effect must be tested using the advertiser’s own data.

For advertisers, the priorities remain accurate event transmission, user matching, and avoiding duplicates.

Why This Update Matters

Adding referrer_url and metadata.order_id makes Reddit’s server-side conversion transmission more structured. The first field helps preserve the context of the page preceding the conversion; the second links the ad event to an order in the advertiser’s system.

These fields are especially useful for e-commerce platforms and agencies with custom integrations. But they do not replace the Reddit Pixel, conversion_id, or existing attribution mechanisms. Their value is primarily technical: easier diagnostics and better control over the quality of conversion data.