One way to do it is to have certain ad spots in your app which sponsors or advertisers can display their banners, images, etc, They would pay per month or for a set of months to have their brand promoted.
For example, you can have like two to three spots on the homepage, of course, these will cost more, not sure how your app is laid out, but pick a few other spots that have a good amount on eyes on them and offer those as ad spots as well.
Either they give you the graphics or you create it (extra fee). You would then upload them as images, add a CTA, with a link behind them. You can track the clicks as well.
Since this would be displayed throughout the app you can create one sheet which has all the ads, and descriptive info then create a relation on each tab’s sheet back to this sheet. That part I’m not to verse in, but I believe that’s how you would display them.