I am building something for indian market which will have subscripotion and that too at 2 levels. One is platform subscription and another is AI subscription which is usage based. I would prefer SDK/webhook integratoin. Payment is defintely required for the launch. And YES it needs to be compliant with indian invoicing system including GST etc. I hope this helps

A subscription service sounds interesting! Depending on the timing, we might jump on board or use a different provider (for now), though.

1. subscriptions and user-to-user
2. launch no, growth yes (sponsorships are hard to get in Germany, but we're working stuff out as we go)
3. modular subscriptions (they pay us), sending money (we pay them) and transferring money while keeping a handling fee (I'm not deep into legal stuff, but I could imagine some specialities there). All of the transactions have to be logged, filterable and exportable for our tax declaration.
4. Paypal and Credit Card as international offers. Would love more regional stuff as well, like Wero and Klarna for (some of) EU
5. pretty sure we'll need VAT. We haven't contacted any lawyers, yet, but will have a talk about that soon
6. web-only during beta, then also mobile. We're currently on NextJS, but for mobile we'll have to use a different framework of course. I'd love a headless library (SDK) for TypeScript (client + server), Swift (client) and Kotlin (client).
7. would love to have a Rust SDK (client + server) as well! I'm eying Dioxus for toy projects for now, but who knows, it might go places...