I’m building a Tenant Application with a Flutter frontend backed by ASP.NET Core (Minimal APIs/Carter), SQL Server, and Dynamics 365 APIs. I’ve received my Sadad merchant credentials, and before wiring everything into production I want to be 100% sure the full payment flow is correct. I’m looking for one-on-one mentoring/guidance from someone who has real hands-on Sadad integration experience (not theoretical). The goal is to implement Sadad end-to-end: Pay button → invoice/order creation → redirect/hosted payment page (or secure WebView) → callback/webhook → verification → reservation status update, including a proper payment state machine + idempotency to prevent double-payments and double-bookings. The immediate focus Primary focus is the Flutter + overall flow correctness, but I also need you to guide the backend contract (API endpoints, webhook verification, database updates). I control the ASP.NET Core backend and can expose any endpoints you recommend. What I need help with: Building the request payload correctly (and signing/encrypting if required by Sadad) Redirecting to Sadad hosted page (or secure in-app WebView if you’ve done it safely) Handling redirect/callback in Flutter correctly Implementing server-side verification and updating PropertyReservationStatus (we use it to hold/lock payment attempts per user) Ensuring idempotency, safe retries, and robust status transitions Must have Real Sadad integration experience (please mention what flow you implemented: hosted page/API/webhook) Strong with webhooks/callback verification, idempotency, and payment state machine design Strong in ASP.NET Core (Minimal APIs/Carter), EF Core, SQL Server Ability to do code reviews + step-by-step guidance Bonus (nice to have) Guidance on a background service to automatically release expired payment holds Flutter integration patterns and secure WebView handling (if applicable) What I’d like from you 1–2 screenshare / pair-programming sessions to walk through the integration step-by-step A concise Flutter code snippet (or small sample) that completes a Sadad sandbox transaction, with comments Best practices for: token storage request signing / encryption redirect handling webhook security + replay protection Availability this week (ASAP) — I want to start immediately if time zones allow No agencies — I want to speak directly with the developer who has shipped Sadad in production. We will pay well for the right person. If you’ve shipped a Flutter app already processing live Sadad payments, please message with a brief summary of your integration approach and what parts you can guide (Flutter, backend, webhook verification, idempotency, etc.).