Handling a 402 from Skavio x402 MCP Without an Infinite Retry Loop
A 402 response from a Skavio x402 MCP paid tool is not a transient error to retry after a short backoff. It is a deliberate payment gate. The useful client behavior is to stop the generic retry loop, inspect the challenge through the published x402 documentation, obtain explicit approval, and allow a retry only after a documented payment-state transition. The exact challenge fields, MCP tool names and retry semantics belong in the documentation, not in guesses.
A 402 is a payment gate, not a transient outage
A generic HTTP client often has one retry policy for everything. That is the wrong shape for a 402 from a paid x402 tool. Treating the response as a temporary infrastructure error can produce repeated payment attempts, noisy logs and ambiguous state. The safer design is a branch: the normal request path stops, and a payment decision path begins. That path should be owned by your application, not an unbounded background loop.
- Stop the automatic retry loop as soon as a 402 is recognized.
- Do not classify a payment challenge as a 5xx-style failure or as a generic validation error.
- Use the published Skavio x402 documentation as the authority for the challenge and the next permitted action.
Keep tool discovery separate from a paid invocation
Skavio x402 MCP is developer-facing MCP and x402 v2 verification for native Circle USDC, public chain inspection and conditional Base USDC payment challenges. Tool discovery and payment are distinct actions. A discovery request should not be logged, retried or described as a paid tool invocation. This separation matters for auditability: it lets a developer confirm what the client can see before any payment decision is made.
- Use discovery to understand the published tool schema and capabilities.
- Do not treat a discovery response as a purchase or a settled call.
- If a paid tool invocation returns a 402, record it as a payment event, not as a discovery result.
A bounded client policy: stop, classify, approve, transition
The client should have an explicit payment state machine. On a 402 it records the event, classifies the challenge against current documentation, and stops. If the challenge is unsupported, stale, on the wrong network, or ambiguous, the client fails closed. If it is potentially valid, the client asks a human user or owner for approval before any payment attempt. A retry is allowed only after a documented payment-state transition, not after a fixed number of sleeps.
- Fail closed on unsupported, stale, wrong-network or ambiguous challenges.
- Require explicit user or owner consent before an autonomous agent pays.
- Keep retries bounded, and make the default outcome of uncertainty a structured error.
- Do not mark the tool call complete from a wallet signature alone; a signed payment challenge is not independently settled revenue.
- Re-check current commercial availability and documentation before enabling live payment in production.
Fail closed with an audit trail that is useful, not revealing
An uncertain payment state should produce a controlled failure, not a fabricated confirmation. The client should return a structured error that distinguishes unsupported challenge, approval not granted, payment not attempted, payment attempt unresolved, and documented retry allowed. Logs should contain enough context to investigate the request without exposing wallet secrets or private signatures. Keep payment evidence separate from the result of the paid tool.
- Never log private wallet signatures, seed material or bearer secrets.
- Do not present a sample wallet address, transaction hash or signature as a real customer payment.
- Reconcile failed calls in a separate payment-state record, and verify paid output against the original request parameters.
- Point operators to the current Skavio x402 MCP documentation when a challenge cannot be classified.