CTV-to-Mobile retargeting conversions occur when Mobile app users who have become inactive are identified on their CTV device. An ad is shown on CTV to re-engage them, leading to a conversion back on their mobile device.

This is how the tracking happens step by step:

The client provides an audience of inactive mobile users, either by uploading it to the system or sharing it dynamically through the MMP DMPs.
MMP provides an impression tracker specific for CTV Ads or prepared for IP matching.
mediasmart places the ad on the CTV of inactive users and retrieves the household IP address. Then, it sends it to MMP with the trackers. We retrieve the household IP address using different approaches depending on the type of inventory (SSAI supported). We filter the bid stream to maximize matching IP addresses in CTV Ads for maximum scale.
Attribution will happen on the MMP side, according to the MMP settings. User downloads the app on a Mobile device and MMP attributes:
a. Mobile app events based on IP matching to TV ads, and
b. Deterministically (IDFA, GAID) to mobile-synced ads.
Note: as the campaign only serves on CTV, attribution will only be View-through (VTA), as there are no clicks on CTV.
mediasmart counts MMP conversions in real-time and assisted conversions when it finds a household matching but no MMP attribution. mediasmart can automatically suppress users who have already converted.
Note: Fully validated IPs are needed to properly attribute. When non-attributed conversions are sent by MMP.
Check how this works on each of our partners:

How CTV App tracking works