The artist must be a lead artist on a track, as opposed to a feature on another artist's album. Releases by a group that this artist is a part of are encompassed within this. To be clear, as long as the artist is a lead artist, it doesn't matter if the track is or later is a track on another artist's album -- that track is included in the Payout Criterion. If multiple sources describe the lead/featured artists differently (e.g. the artist is listed as a feature on YouTube but a lead artist on Spotify), Spotify will be used to break any doubt.