Client

Unlike the server-only SDKs in some languages, Rust also ships the paying side, via the protocol-layer crate re-exported at solana_pay_kit::mpp. The flow is: read the 402 challenge, sign a credential for it, and replay the request with the credential.

Pay a challenge

use solana_pay_kit::mpp::client::{build_credential_header, parse_challenge};
use solana_pay_kit::mpp::solana_keychain::memory::MemorySigner;
use solana_pay_kit::mpp::solana_rpc_client::rpc_client::RpcClient;

// 1. Parse the MPP charge challenge from the 402 `WWW-Authenticate` header.let challenge = parse_challenge(www_authenticate)?;// 2. Sign a payment credential and replay the request with it.let authorization = build_credential_header(signer, rpc, &challenge).await?;let res = reqwest::Client::new()    .get("https://api.example.com/quote")    .header("Authorization", authorization)    .send()    .await?;println!("{}", res.text().await?);

Auto-pay guardrails

For unattended clients, build_charge_transaction_with_options (and build_credential_header_with_options) add guardrails before signing:

• a spending cap (max_amount_base_units),
• an expected-network pin, and
• a refusal to sign unknown Token-2022 mints unless explicitly opted in.

Or just use the CLI

For most cases the pay CLI is the simplest client — it handles the wallet, signing, and the 402 retry transparently, against any pay-kit server:

pay curl http://127.0.0.1:4567/quote