Project architecture sanity check

My app is quite simple. I want a react app front end where the user can:

subscribe to pay $ per month via stripe integration

I know when it comes to stripe you guys have a great tutorial https://appwrite.io/docs/tutorials/subscriptions-with-stripe/step-1

i know that i need to have stripe secrets in a appwrite function to create a checkout session and all that

So in my head i have the following

react app hosted on vercel - is has the appwrite js sdk https://github.com/appwrite/sdk-for-web

the react app will need to call my appwrite function to generate a stripe checkout session to do the needed stripe stuff

My concern is that since appwrite functions are open to the world that anyone could generate a checkout session or what not - in a perfect world i only want my appwrite function to be callable from my website

TL;DR

Developers are discussing project architecture and whether to have separate projects for dev/staging/prod. One developer is worried about back charges. Another developer suggests setting Function Permissions to only allow logged in users. The main developer wants a simple React app with user sign up/login/logout, email/password changes, password recovery, and a subscription payment via Stripe. They mention a helpful tutorial for integrating Stripe with Appwrite. Their proposed architecture includes a React app hosted on Vercel with the Appwrite JS SDK. They are concerned about the security of their Appwrite function and want it to only be callable from their website. No solution is provided in the