RTB Without Caller Number via SIP

What's new

Publishers can now make RTB requests without providing a caller number. When the postback key has "Allow no caller number" enabled and no caller_number is passed, Retreaver returns a SIP address for the inbound_number instead of a phone number:

sip:2e11554b-9bc7-4a19-b4b5-a79dc79ccce1@retreaver-rtb.sip.twilio.com

The UUID in the address uniquely identifies the reservation. When the publisher dials this SIP address, Retreaver recognizes the UUID and connects the call to the reserved buyer.

Learn more in the Retreaver Real-Time bidding guide

What you should know

When no caller number is provided, some capabilities are reduced:

• Geographic matching may not work. Retreaver uses the caller's area code, state, and ZIP to match calls to the right buyer. Without a caller number, none of this information is available unless the publisher passes it explicitly as parameters in the request (e.g. caller_zip, caller_state).
• Caller lists cannot be checked. Suppression lists and acceptance lists rely on the caller's phone number. Without it, there is no way to determine if the caller is blocked or pre-approved.
• Buyer matching is limited. The only thing Retreaver can confirm is whether a buyer exists and is potentially available — not whether this specific caller would actually be accepted by the buyer.

Because of these limitations, it's important that the publisher, the Retreaver client, and the buyer agree on what information will be provided with each request. Exactly what needs to be synced depends on the parties involved and what the buyer expects in order to return an accurate availability or bid.

SIP credentials

To send calls to a SIP address, the publisher needs SIP credentials (username and password) to authenticate with the SIP domain. These credentials are provided by Retreaver.

You have flexibility in how you distribute them:

• One credential per publisher — each publisher gets their own username and password, giving you visibility into which publisher is making each call.
• One credential for your whole account — all publishers share the same username and password, which is simpler to manage but provides less granularity.

The credentials authenticate the SIP connection only — they do not determine which campaign or buyer the call is routed to. Routing is determined entirely by the reservation UUID in the SIP address.

Why it matters

Previously, RTB requests without a caller number were not accepted. This means publishers who check availability without a caller number no longer need to flood the space with hundreds of thousands of fake numbers, and the SIP address provides a clean, traceable identifier for each reservation.