# Traffic Source Postback
Before adding S2S postback, look for the answers:
- Does the traffic source support S2S postbacks?
- What placeholders traffic source allows using?
- Where to get personal Postback URL?
Paste your personal Postback URL to Postback URL
field.
Replace the value of click ID to {external_id}
(it's a placeholder).
For example, your personal Postback URL is https://adnetwork.com/postback?aff=99&uid=CLICK_ID
.
The final URL as follows:
https://adnetwork.com/postback?aff=99&uid={external_id}
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