> ## Documentation Index
> Fetch the complete documentation index at: https://docs.apostra.com/llms.txt
> Use this file to discover all available pages before exploring further.

# Your default advertiser

> What a source's default advertiser is, which ad servers have one, how to set it on the ad-server source page, and how the Advertiser for live buys check uses it.

A live buy books against an advertiser on your ad server. A buyer you have mapped to an advertiser books
there. Every other buyer books on the source's **default advertiser**, the catch-all for buyers with no
mapping of their own. [Why you approve and map buyers](https://docs.apostra.com/v3/seller-why-approve-and-map-buyers.md) explains the
mapping.

## Which ad servers have one

Google Ad Manager, FreeWheel and AdsWizz sources each have a default advertiser. Each ad server keeps it in
its own place, and Apostra writes it there for you.

SpringServe has no advertiser in its model, so it has no default advertiser. The check described
[below](https://docs.apostra.com/v3/seller-default-advertiser.md#the-advertiser-for-live-buys-check) never applies to it.

## Set it on the ad-server source page

Open the ad-server source page and use **Set default advertiser**. It lists the advertisers on your ad
server and writes the one you pick. It works the same way for Google Ad Manager, FreeWheel and AdsWizz.

Two differences follow your ad server, not Apostra:

* **Search.** Google Ad Manager serves a searchable advertiser cache, so typing narrows the list at the
  source. The other ad servers return a bounded page of advertisers, which the page filters in place.
* **Creating an advertiser.** Only Google Ad Manager lets Apostra create an advertiser for you, so the
  option to create one appears there. On the other ad servers, create the advertiser in your ad server
  first, then pick it.

An inventory sync can succeed even when your ad-server credential cannot see any advertisers, because
inventory and advertisers are separate permissions. If the advertiser list is empty, check that the
credential can read advertisers. For Google Ad Manager, see [Google Ad Manager access](https://docs.apostra.com/v3/seller-gam-access.md).
A healthy inventory count is not proof that advertiser access is set up.

## The Advertiser for live buys check

A live buy has to book against an advertiser, so your [setup checklist](https://docs.apostra.com/v3/seller-readiness.md) has an
**Advertiser for live buys** check (`esa_live_advertiser`). Without a resolved advertiser every buy outside the sandbox fails, so a
storefront that reported itself ready would be telling you something untrue.

The check reads the advertiser from your ad server, not from a copy Apostra holds. Setting one clears the
check on your next read, with nothing else to do.

* **Sandbox tests still run.** A no-spend test books on a separate sandbox advertiser and never uses the
  default advertiser, so the test is admitted while the check is open. A passing sandbox test is not
  evidence that live buys will work, because the two use different advertisers.
* **Several ad servers keep the storefront live.** If you sell through more than one ad server, the check
  blocks only when none of them can route a live buy. When one is missing an advertiser and another can
  still take live buys, the check names that ad server as a warning, and your storefront keeps selling the
  inventory that works.
* **Ad servers with no advertiser are exempt.** SpringServe has no advertiser in its model, so the check
  never applies to it.
* **Where the check sends you.** For Google Ad Manager, FreeWheel and AdsWizz the check links to the
  default advertiser action on the ad-server source page. If an ad server with a default advertiser has no
  such action on the page, the check asks you to contact Apostra instead of pointing at a control that is
  not there.


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