Push notifications can drive return visitors and ad revenue. Do you use services like OneSignal or PushEngage? Have they boosted your earnings?

To use push notifications for increasing revenue, send targeted, personalized messages about promotions, new content, or exclusive offers. Segment your audience based on behavior, and ensure notifications are timely to drive traffic and conversions.

There are push ad networks that pay you when your visitors subscribe to them and views the ads, however, I have never used them as I consider them to be intrusive.