This isn't similar to indulgences at all.
Indulgences were essentially a way to buy absolution. If you were wealthy, you could willfully sin and then buy back your admission to heaven.
This app is not that. It's a faith-based meditation guide. It's often compared to HeadSpace, including by its founder[1].
1. https://www.pillarcatholic.com/p/i-tried-the-hallow-app-for-...
