Payment Gateway integration for Flutter in India

Question

I am trying to integrate PhonePe Payment gateway with my flutter application so I need your help with this.

Backdrop

There is no flutter sdk for PhonePe or other available PG providers so we have to do things the hardway.

As my per my understanding we have multiple approach to go with this

1. Create a webview in flutter and do the integration on a PHP server(in laravel as there is a Youtube tutorial about it and capture its response in flutter after txn is done) but here I have to abondon the Firebase ecosystem which I have been using till now.
2. Create Firebase cloud function in nodejs( which I have no idea)
3. Switch to CCAvenue as there is a great post available with how to integrate https://dev.to/djsmk123/flutter-cc-avenue-payment-gateway-integration-ft-php-1nj7 But again, we are leaving firebase ecosystem and we have to pass firestore data to php server, maintain it also, Plus ₹1000 yearly maintenance also.
4. Use Stripe Payment which has a tighter integration with firebase https://firebase.google.com/docs/tutorials/payments-stripe But I am don't know if UPI is acceptable with stripe and In India UPI is lifeline.
5. Wait for Other payment gateway providers to launch their sdk, but I doubt it will happen anytime soon.
6. Wait for prominent players like Paytm, RazorPay to start onboarding. But this could happen tomorrow or might not happen till next year. (So this is not possible)

If there is anybody with experience with payment integration with flutter and creating checksum in server. Then please share your experience and guide me how should I proceed now.