I created Smart Receipts for receipt tracking and OCR a few years ago. I worked as a traveling consultant and needed to track receipts on a weekly basis, and I got tired of manually typing in the data.
It's available on both Android and iOS for download here:
I'm in the exact same boat - about 75-80% of my income comes from the paid version of the app. The free version mostly serves as a staging ground to increase adoption and encourage users to upgrade to get rid of the ads.
I make about $600/month between ads on the free version and sales for the paid version; not enough to quit my full-time job but a nice monthly supplement.
It's available on both Android and iOS for download here:
https://smartreceipts.co/download
It's also open source:
https://github.com/wbaumann/SmartReceiptsLibrary https://github.com/wbaumann/SmartReceiptsiOS