The fantasy versus the reality
The passive-income story, ship an app, watch ad revenue roll in, is built on the top of the charts, where games with millions of daily users make it work. At small-business scale that math does not close: the audience is measured in thousands, not millions.
The realistic model is the opposite of passive: the app is a retention channel that makes the existing business more valuable, more orders, more bookings, more repeat visits, and the money comes from that lift, not from the app itself.
The revenue options, honestly rated
One-time purchase or subscription works when the app is the product, rare for a business app. In-app ads work only with volume, and on a small audience they annoy your best customers for pennies. The reliable earners are the transaction and retention loops: order from the app, book from the app, get the push that brings you back.
Push notifications are the most impactful feature in this list. A well-timed message to an installed audience converts measurably better than the equivalent email, and it costs nothing per send.
What to measure
Track three numbers: installs that came from a real channel, how many of those open the app twice, and how many complete the money action, order, booking, or contact. If the second and third are healthy, the app is paying for itself even before you price it.
That is the honest version. The app is infrastructure for revenue you already know how to earn, not a revenue machine on its own.