Okay, now you know your idea has some potential to make app passive income. Start doing some homework. Download the app and use it. Get familiar with it. This is where you put on your creative thinking app. It’s not your app idea that has to be completely innovative. It’s the execution of it. A great idea will most likely already have a few versions of it. Read the customer reviews. See what they like. More importantly, see what they are complaining about. This will give you essential information on your target audience. It’s almost as if you’re skipping version 1 and going straight to version 2 of your idea.

Ebooks are one of my favorite sources of passive income. Now, you can do this the simple way and just publish it on Amazon's KDP. Or, you can go all out and build yourself a book funnel. Book funnels are powerful, but they won't be fully passive. For example, if you do a free-plus-shipping offer for your ebook (converting it into a physical book), you'll need to create some one-time offers (i.e. extra training) and up-sells (i.e. an audiobook). But, a book funnel can be very powerful.
Last, but certainly not least, you could get yourself a cash back credit card. This would enable you to make some extra cash by spending money that you were already going to spend. You even have a ton of options to choose from, depending on your spending style. So whether you spend a lot at restaurants, grocery stores or traveling, there will be a card that can earn you cash back. Usually you can earn 1% cash back, but some cards even offer 5% on special categories.
I have only dabbled in drop-shipping before when I had an eCommerce platform 6 years ago or so. I think it is something that you could do on the side, but you would want to do in depth research on the industry you want to get into before setting up shop. It may be a little less passive up front, but over time you could take your hands off the wheel.