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Backend overview

As a developer you should think of the backend as the single source of truth for payments. With x402 the provider handles actual transaction execution (on-chain or relayed), but your backend is where you:
  • build and store paymentSession objects (paymentId, item, amount, user),
  • produce the signable payload that clients must sign,
  • verify signatures the client returns,
  • call x402 endpoints to finalize a payment,
  • process webhooks, and
  • grant game items / update order state.
Gx402’s approach: we provide middleware blueprints and opinionated server patterns (Express examples in the repo) so every platform (Unity, Unreal, WebGL, Telegram, Farcaster, Mobile) talks the same language to your backend. That reduces cross-platform bugs and ensures consistent auditing.

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Responsibilities (server-side)

  • Session lifecycle: create → pending → finalized/failed.
  • Signature verification: check that the signature matches the expected wallet address.
  • Idempotency & replay safety: prevent double fulfillment.
  • x402 integration: call x402 create/confirm endpoints when appropriate.
  • Webhooks: verify and reconcile async events from x402.
  • Auditing: persist paymentId, orderId, txHash, timestamps, and user ids.

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Quick model for you

Platform (Unity/Web/Unreal) → Middleware → Your Backend (paymentSession, verify) → x402 API
Tip: keep the server-side logic intentionally simple: build a deterministic payload, persist session state, verify signatures, call x402, then respond. Complexity belongs in the server.