Jon Schneider was mindlessly scrolling TikTok when a video caught his eye. It showed the actor Mark Wahlberg and “this guy who kind of looks like Jesus,” and they were inviting viewers to join them in prayer.

Mr. Schneider, 35, thought it was a movie promotion. In reality, it was an ad for Hallow, a pay-to-pray app that offers Bible readings and sermons narrated by clergy and celebrities, including the former N.F.L. star Brett Favre and Madison Prewett of “The Bachelor” fame.