Keep it free for everyone.
In My Stash is free, and it stays free — no ads, no upsells, no selling your data. It's built for people counting every dollar, and plenty of its users shouldn't spend a cent on it. If you're doing okay and the app has earned a place in your pocket, you can chip in so it keeps running for the people who aren't.
Supporting unlocks nothing. Every feature is already yours — that's the point. Contributions cover the servers, the security work, and keeping the lights on, so the app never has to charge the people it's built for.
Payments are handled by Stripe. In My Stash is an independent app, not a charity — contributions aren't tax-deductible. Cancel a monthly contribution anytime from your Stripe receipt.