create-typescript-x402-client

Create an x402Client, call registerExactAvmScheme with your ClientAvmSigner, then pass fetch and the client to wrapFetchWithPayment from @x402-avm/fetch. The wrapped function intercepts 402 responses, signs the payment transaction, and retries with the PAYMENT-SIGNATURE header.

Use wrapAxiosWithPayment from @x402-avm/axios after registering the ExactAvmScheme on an x402Client. Add your own interceptors first and call wrapAxiosWithPayment last, since the payment interceptor should run after other response interceptors.

Yes, implement the ClientAvmSigner interface using @txnlab/use-wallet or PeraWalletConnect. The signer's signTransactions method delegates to the wallet's signing function, returning signed blobs for the requested transaction indexes.

AVM_PRIVATE_KEY must be a Base64-encoded 64-byte key consisting of a 32-byte seed plus a 32-byte public key. Derive the address with algosdk.encodeAddress(secretKey.slice(32)), never from the first 32 bytes.

This error means the server requested a payment network for which no scheme was registered. Call registerExactAvmScheme(client, { signer }) before wrapping fetch or Axios, or use the algorand:* wildcard in config-based setups to match any Algorand network.

Register a PaymentPolicy on the x402Client that filters requirements by amount, for example keeping only requirements where BigInt(r.amount) is below your limit. Policies run in registration order, and you can also abort payments in an onBeforePaymentCreation hook.