The latest report from SensorTower shows that app purchases generated a revenue of US$39.7 billion in the 1st 6 months of 2019. This impressive figure also represents a 15% year-on-year increase in the same kind of spending. The Apple App Store accounted for 64% of these takings.
https://www.notebookcheck.net/Nearly-US-40-billion-was-spent-on-apps-in-the-1st-half-of-2019.427036.0.html