Set a default code for unfilled requests

What it is and why

Default code is the markup the ad server returns when nothing at all filled the request: the placement-level fallback, typically another ad source’s tag. It is separate from the daisy chain, which only orders the demand Epom already has, and from a banner passback, which hands an impression back from a tag Epom served. This page is one of the three stages of Set up daisy chaining and passbacks; it also covers the video case, where a placement has no default code and the fallback is set up as bottom-of-stack demand instead.

Example. A news site’s article MPU carries a backup network’s tag in Default code, with $$RANDOM$$ as its cache-buster. When every linked banner is capped for a visitor, the Universal JS tag receives that backup tag instead of a blank slot. The site’s pre-roll placement gets a Backfill — Partner Video campaign on the House ads priority with a Third Party VAST tag URL banner, which only receives the requests nothing above it could serve.

Typical scenarios

You want	Set	Where
A backup network’s tag when nothing fills a site placement	The tag in Default code, with $$RANDOM$$ as cache-buster	placement → Basic info → Advanced settings
A fallback VAST tag on a video placement, which has no default code	A House ads campaign with a Third Party VAST/VPAID Tag URL banner, linked at the bottom of the stack	a backfill advertiser and campaign
The player to try several partners in turn	A VAST waterfall rather than one fallback	VAST waterfall across several networks

Step by step

Set a default code for unfilled requests

1. On the same placement, open Basic info → Advanced settings (collapsed by default). Default code is there on Site, Mobile site and Non-standard site placements only, and only for a role holding Placement Default Code.

2. Paste your fallback markup into Default code. Epom substitutes macros into it before returning it, with the same processor as banner markup: $$RANDOM$$ and $$TIMESTAMP$$ as cache-busters, $$PAGE_URL$$, $$COUNTRY$$, $$PLACEMENT_ID$$, $$CHANNEL$$, custom parameters and the rest of the request, page and placement set. No creative was chosen, so banner, campaign and advertiser macros and the click URLs come out empty; a recognised macro that cannot resolve is removed, an unrecognised token (a partner’s own [timestamp]) is left as written. See Macros.

   

3. Click Save. Whether the code is ever returned depends on how the tag calls Epom — see When the default code is returned.

A fallback VAST tag for a video placement

A video placement has no Default code field, so a third-party VAST tag that should play “only when Epom has no ad” is set up as demand at the bottom of the stack:

1. Create an advertiser and campaign for the fallback (for example Backfill — Partner Video) with delivery priority House ads or Non-guaranteed, below every campaign that should win first. Priority tiers are tried top-down, so this campaign only gets requests nothing above it could serve.
2. Add a video banner of type Third Party VAST/VPAID Tag URL with the partner’s tag.
3. Add the campaign’s targeting — for example only the countries the partner buys.
4. Link the banner to the video placement.

The fallback’s impressions are counted and priced like any other banner’s — by its campaign’s Pricing card — so give it the price you agreed with the partner, or none for a pure house fill. To let the player try several partners in turn, see VAST waterfall across several networks.

Caveats and exceptions

Default code on other placement types. The console draws the field on Site, Mobile site and Non-standard site placements only. A default code stored on another type anyway — the REST API accepts defaultCode for a role holding Placement Default Code — is never returned for an Application placement, never for a VAST/video request, and never from the native JSON endpoint; a Video or Native placement only sees it on the request paths listed under When the default code is returned.

Which request paths return the default code, why the CPM threshold does not “trigger a passback”, the auto-refresh on a no-fill and who can do this are on Set up daisy chaining and passbacks.

Not working?

Symptom	Check	Where
The default code never fires	The request path does not carry it (Application, VAST, native JSON, overlay, API v4, S2S, unknown key); or the field is on a placement type that has none	When the default code is returned; the placement type
The default code fires but the backup tag is cached	No cache-buster in it	put $$RANDOM$$ or $$TIMESTAMP$$ in the tag

The No ads column and a missing card are on Set up daisy chaining and passbacks; a slot that stays empty for other reasons is on Low fill rate.

Reference

The Default code field, the request paths that return it and the full list of reasons a request ends without a banner are under Fallback fields outside the card on the hub and on Daisy chaining and passbacks reference; the REST field defaultCode is under Over the API.

Related pages:

• Set up daisy chaining and passbacks
• Order a placement’s demand into a daisy chain
• Let a third-party tag pass the impression back
• Daisy chaining and passbacks reference
• Create a placement — where Default code lives
• Macros reference
• Set a site CPM threshold
• Low fill rate