It might be hard to believe but this short book really works.It worked for me and about a dozen friends and family including my dad in his 60s. Read the reviews section for it on Amazon, review after review stating that the book changed their lives.
Edit: There are now almost 7000 reviews with the vast majority saying the book worked. The last time I checked about 10 years ago there was only 400 or so and that was very impressive then.
Not OP, but there's not much to do about them - best way is to enter manually in the app at the time of purchase or write them down in a notebook and enter them in batch once in a couple days or per week.
If your cash spending is sufficiently small that you don't care much to tracking each cash transaction individually, you can just track money as a category instead of an account - just record an outflow transaction in your bank account when you withdraw.
I don't use ynab anymore, but when I did, I usually just didn't include cash in it. I almost never use cash, and so it made sense to just deduct the money when it became cash.
I would licence it and pitch it to him as a SaaS. Bonus or a raise won't get you as much value for your product but this way you can get another stream of monthly income and maybe he knows other shipping companies that you can sell your product to. Good luck
