Opting into the Social Media Monetization extra ensures you receive royalties from videos on YouTube, TikTok, Instagram, or Facebook that feature your music at upload (user-generated content, or UGC).
If your song is embedded in a video during upload—not added later from a music library—you'll receive a share of the ad revenue (minus 20%) directly into your eMastered royalty balance.
To activate it, make sure it is checked on the "review," page of your distribution submission form:

Once applied, eMastered syncs your track to UGC matching systems to track usage and earnings across platforms.
Note that This Add On renews annually per release.