Reddit CAPI (Server-Side)

Reddit’s Conversions API (CAPI) exists, works, and is significantly less polished than Meta’s or TikTok’s. If you are running Reddit ad spend where attribution actually matters — B2B tech, gaming, crypto, niche communities — CAPI pays for itself by recovering conversions the client-side pixel misses. If Reddit is a rounding error in your media mix, skip it.

Valid as of April 2026, Reddit Conversions API v2.

Why server-side for Reddit

Reddit’s client-side pixel has the same ad-blocker and ITP exposure as every other ad platform, with an added wrinkle: Reddit’s audience skews toward technically literate users running uBlock Origin, Brave, and Firefox with strict tracking protection. A meaningful share of Reddit converters are actively blocking the client-side pixel.

CAPI recovers those conversions by sending events from your server — where no ad blocker can reach — keyed on Reddit’s click identifier (rdt_cid) which arrives in the landing URL.

When it is not worth it: Reddit’s measurement is materially less accurate than Meta’s or Google’s regardless of CAPI. If your campaigns can’t tolerate ±20% attribution noise, Reddit probably isn’t the right channel in the first place. And Reddit’s conversion APIs have no public test-events UI, so debugging is slower than on other platforms.

The event model

Reddit CAPI v2 accepts one or more events per request at a per-pixel endpoint.

Required per event:

Field	Notes
event_at	ISO 8601 timestamp (NOT Unix epoch)
event_type.tracking_type	One of Reddit’s standard types
click_id	The rdt_cid value — strongly recommended
conversion_id	Your dedup key for event-level matching

Standard tracking_type values: PageVisit, ViewContent, Search, AddToCart, AddToWishlist, Purchase, Lead, SignUp, Custom.

Match keys:

Field	Hashed?
user.email	SHA-256
user.external_id	SHA-256
user.aaid	No (mobile ad ID)
user.idfa	No (iOS IDFA)
user.ip_address	No
user.user_agent	No
user.screen_dimensions	No

Caution

Reddit’s documentation hints at internal processing concepts (“advertiser event processing”) that are not exposed as public API parameters. If you see references to aepp or similar in community templates, those are client-template conveniences, not fields on the Reddit API. Stick to the v2 request shape below.

Setup in sGTM

Reddit has no official sGTM community template. You will build a Custom Template or a Custom Image Tag with sendHttpRequest.

1. Create a Reddit developer app at Reddit Ads Manager → Business Info → API Access. Request the conversions.write scope. You will receive a client ID and client secret.

2. Generate a long-lived OAuth access token. Reddit’s tokens are refreshable; in practice, store the refresh token as an sGTM constant and have your sGTM template call the token endpoint when the access token expires. For low-volume use, generate an access token manually and set a calendar reminder.

3. Get your Reddit Pixel ID from Ads Manager → Conversions. It’s a UUID.

4. In sGTM, create a new Custom Template. The skeleton:

   const sendHttpRequest = require('sendHttpRequest');
   const getAllEventData = require('getAllEventData');
   const JSON = require('JSON');
   const sha256Sync = require('sha256Sync');
   
   const event = getAllEventData();
   const url = 'https://ads-api.reddit.com/api/v2.0/conversions/events/' + data.pixelId;
   
   const body = {
     events: [{
       event_at: new Date(event.timestamp_ms).toISOString(),
       event_type: { tracking_type: data.trackingType },
       click_id: event.rdt_cid,
       conversion_id: event.event_id,
       user: {
         email: event.user_data && event.user_data.email_hash,
         external_id: event.user_data && event.user_data.external_id_hash,
         ip_address: event.ip_override,
         user_agent: event.user_agent
       },
       event_metadata: {
         currency: event.ecommerce && event.ecommerce.currency,
         value: event.ecommerce && event.ecommerce.value,
         item_count: event.ecommerce && event.ecommerce.items && event.ecommerce.items.length,
         conversion_id: event.ecommerce && event.ecommerce.transaction_id
       }
     }]
   };
   
   sendHttpRequest(url, {
     method: 'POST',
     headers: {
       'Authorization': 'Bearer ' + data.accessToken,
       'Content-Type': 'application/json'
     }
   }, JSON.stringify(body));

5. Configure the tag’s input fields for Pixel ID, Access Token (stored as a Constant variable), and Tracking Type (mapped per event).

6. Read rdt_cid from the landing cookie via a Cookie Variable in sGTM, propagated through GA4 as an event parameter.

Raw HTTP shape:

POST https://ads-api.reddit.com/api/v2.0/conversions/events/<pixel_id>
Authorization: Bearer <oauth_token>
Content-Type: application/json

{
  "events": [{
    "event_at": "2026-04-20T12:34:56Z",
    "event_type": {"tracking_type": "Purchase"},
    "click_id": "<rdt_cid>",
    "conversion_id": "evt-ORDER-123-1713571200",
    "user": {
      "email": "<sha256>",
      "external_id": "<sha256>",
      "ip_address": "203.0.113.45",
      "user_agent": "Mozilla/5.0 ..."
    },
    "event_metadata": {
      "currency": "USD",
      "value": 79.99,
      "item_count": 2,
      "conversion_id": "ORDER-123"
    }
  }]
}

Event mapping from the Reddit Pixel

GA4 event	Reddit tracking_type	Notes
page_view	PageVisit	Optional; client-side already covers it
view_item	ViewContent	Pass product in event_metadata.products
add_to_cart	AddToCart	Pass value, item_count
purchase	Purchase	The critical one — carry order_id as conversion_id metadata
generate_lead	Lead
sign_up	SignUp
search	Search	Pass query in event_metadata.search_query
(custom)	Custom	With custom_event_name metadata

Deduplication with the Reddit Pixel

Reddit’s deduplication is unusual: the primary matching signal is click_id (the rdt_cid), and conversion_id is the secondary per-event dedup key. Window: 7 days.

What this means in practice:

• If both pixel and CAPI fire for the same user’s purchase and both carry the same rdt_cid, Reddit will usually dedup even without conversion_id.
• But relying on rdt_cid alone is fragile — if the click was from an old session, the cookie expired, or the user cleared cookies between click and purchase, rdt_cid on the CAPI side may not match what the pixel sent.
• Always send conversion_id (sourced from your dataLayer event_id) on both sides. On the client-side pixel, that maps to the externalId parameter.

Propagation:

// dataLayer on the thank-you page
dataLayer.push({
  event: 'purchase',
  event_id: 'rdt-' + order.id + '-' + Date.now(),
  rdt_cid: readCookie('rdt_cid'),
  ecommerce: { ... }
});

Client-side Reddit Pixel: pass externalId: '{{DL - event_id}}'. sGTM CAPI: set conversion_id = event.event_id and click_id = event.rdt_cid.

Testing and validation

Reddit Ads Manager → Events Manager → your pixel shows inbound events with a source column (“Pixel” / “CAPI” / “Both”). Latency is 2–10 minutes — longer than Meta or Snap.

Reddit has no test-events mode. Your options:

1. Use a staging pixel (create a separate pixel ID in a test ad account) during development.
2. Filter Events Manager by timestamp during test windows.
3. Check your sGTM Preview mode for the tag’s request/response to confirm the API accepted the event (HTTP 200).

A 400 with no body usually means event_at is Unix epoch (it must be ISO 8601). A 401 means the access token expired.

Common mistakes

Using Unix epoch for event_at

Reddit requires ISO 8601 (2026-04-20T12:34:56Z). A number like 1713571200 is rejected with a 400. Most other CAPIs accept epoch; Reddit does not.

Omitting click_id entirely

Without rdt_cid, Reddit falls back to IP + user agent matching, which has a much lower match rate. Always capture rdt_cid from the URL on landing, store it in a first-party cookie for the ad’s click window, and include it on every CAPI event.

Sending plaintext email in user.email

user.email must be SHA-256 hashed, lowercase, trimmed. Sending plaintext user@example.com silently fails to match (the event is still recorded, but attribution is degraded).

Token expiry with no refresh path

If you generated a manual OAuth token and never wired up refresh, it will expire — typically within a few months — and every CAPI request starts returning 401. Build the refresh into your sGTM template or at minimum set a calendar reminder and monitoring.

Related articles

Reddit Conversion Pixel (Client-Side) The client-side pixel that CAPI supplements — base tag, standard events, and rdt_cid capture.

Meta CAPI (Server-Side) The reference CAPI implementation — cleaner tooling and more mature debugging.

Event Deduplication Across Client & Server Cross-platform cheat sheet for dedup field names, windows, and stable ID generation.

Server-Side GTM Overview The sGTM foundation required for CAPI implementations on any platform.