Fix VPN iOS App In-App Purchases

My VPN iOS app, developed in Rust Flutter, has stopped processing in-app purchases due to Apple's recent transition to StoreKit2. Both the iOS app code and the server-side implementation, which is written in Java and connects to WHMCS, require updates. I need a freelancer who can:

- Update the iOS app to utilize StoreKit2
- Make necessary adjustments to the server-side implementation
- Ensure seamless integration with WHMCS

A strong understanding of Rust Flutter, Java, and WHMCS is essential. Please bid only if you are familiar with all of these.