Server-side verification callbacks are URL requests, with query parameters expanded by Google, that are sent by Google to an external system to notify it that a user should be rewarded for interacting with a rewarded video ad. Rewarded video SSV (server-side verification) callbacks provide an extra layer of protection against spoofing of client-side callbacks to reward users.
Read more at: https://developers.google.com/admob/android/rewarded-video-ssv
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