Currently it's being tested as voluntary but it's set to become required for all citizens.
Besides keeping track of your financial transactions it also keeps track of friends, family members, and groups you support.
Your 'social credit' scores rises or falls depending on whether you're a good citizen who toes the party line or a bad citizen who supports dissident groups outside the official party line.
High social credit scores bring social and political benefits. Low social credit scores means you lose social and political benefits like where you can live and what job you can have.
Watch these two videos. Don't be put off by the animation of the first or the conspiracy theme of the second. This is serious stuff:
Propaganda Games: Sesame Credit - The True Danger of Gamification - Extra Credits
Right now, China has a ‘social credit’ system called, ‘Sesame Credit’.