You already mentioned it, but I would highly recommend RevenueCat. It is free up to $2.5K MTR. After that, just 1% (which is nothing compared to the 15 or 30% that Apple/Google takes from you). They have a first party Capacitor plugin. On top of just IAP, they offer a full dashboard, paywalls, A/B testing, etc. I don’t think paywalls are available yet though with the Capacitor plugin.
I originally went with GitHub - j3k0/cordova-plugin-purchase: In-App Purchase for Cordova on iOS, Android and Windows to save on cost too and rolled my own backend for webhooks and communication with Apple and Google. I thought I was saving money…haha! But in the end, it “cost” more in dev time. It was also more complicated to set up in the app.
With that, I would really consider RevenueCat. Why spend time and worry about IAP and all the little wiggles that Google and Apple have with their APIs (RevenueCat handles all this for you and stays on top of all their changes)? Instead, you could be spending that time on your actual app - adding features, marketing, fixing bugs, etc.