Why isn't third-party activity in Garmin Connect reaching Terra?

Garmin's Wellness API only returns activities recorded natively on a Garmin device.

Garmin's Wellness API only returns activities recorded natively on a Garmin device. Activities imported into Garmin Connect from third-party platforms (Rouvy, Zwift, etc.) show in the Connect UI but are not in Garmin's export feed, so they cannot reach Terra via Garmin regardless of scope, endpoint, or webhook mode.

To capture those sessions, connect the originating platform's provider in Terra directly.