Monetizing nostr apps isn't straightforward.
Its difficult if not impossible to use the existing webs monetizing models since users can easily switch apps.

For examples:
- I could start showing ads but that would slowly annoy my users and if I didn't get new users I would slowly bleed users
- Subscriptions could work. But really only for access to premium or future feature. Not for content ( since I don't control it )
- zap splits might work. But even Lightning isn't really optimized for splitting 1-2% of a payment to a third party

I could go on, but the my point is since I don't own the content in my app or the users that use it. I don't know what I could sell besides my time developing the app