Subscriptions in mobile apps

Say, you have a SaaS. A (react native) app that you'll release to App Store and Google Play. 2 weeks are for free and a user doesn't have to add a card to start the trial.

Now, you want to give them an option to buy the full version in a subscription model. What do you use? Stripe? Or do you HAVE TO use In-App Purchase as per store?

Apple and Google cut 15% as their commission for subscriptions (jumps to 30% once you hit $1M in sales). Stripe cuts 0.5%.
From $$$ point of view, the choice is obvious.

Another benefit of using Stripe would be giving people access to the whole product. I mean, what should happen if a user changes their phone from Android to iOS? I guess they have to kill the subscription in one platform and buy on the new one? (that is probably an edge case).

What if I'll, one day, introduce the project to the web? Should I create a 3rd subscription mechanism then? 😅 (via Stripe).

Sounds like a lot of work so maybe I'm overthinking this here. 🤔
What do you do? What is your experience? Are we forced to use In-App Purchase for subscriptions and this is a lost case?

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I have seen a few topics like that but it didn't find answers that would satisfy me ✌️