Move a bidder server-side and it suddenly cannot recognize anyone, 0% match rate on day one. The fix is cookie sync: a handshake that teaches the server which user is which. Until it runs, server-side demand bids blind.
Server-side bidders’ IDs must be synced through the /cookie_sync endpoint. Cooperative syncing lets bidders share sync slots, so the page is not flooded with sync pixels.
Key idea
A freshly onboarded s2s bidder starts near 0% match rate and climbs as syncs accumulate. It is not broken, it is warming up. Judge it after the sync population matures, not on launch day.
Stored requests
Stored requests are OpenRTB blocks kept on the server and merged into the request via ortb2Imp, so the client sends a small reference instead of a full config. They are central to mobile-app and AMP delivery, where the client cannot carry a heavy Prebid setup.
Quick check
A new server-side bidder shows a 0% match rate on launch day. Broken, or expected?