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1Clear out junk files and repair common Windows errors2Fix the driver behind crashes, sound loss and screen glitches3Repair Windows errors before they cause bigger problemsWhen an x402 payment fails—or a paid service is missing from a marketplace catalog—first identify which stage failed: the HTTP challenge, payment authorization, facilitator verification, settlement, or catalog indexing. A completed settlement does not automatically publish a resource in every facilitator’s catalog.
Start by identifying the failed stage
Record the HTTP status, response body, and x402 headers from both the initial request and the request that submits payment. In the HTTP flow, a server advertises payment requirements in PAYMENT-REQUIRED; the client sends signed authorization in PAYMENT-SIGNATURE; and a successful response may include PAYMENT-RESPONSE. Header details can vary by transport and implementation, so use the response data rather than status alone to diagnose the problem. See the HTTP transport specification and x402 Specification v2.
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- Initial 402 Payment Required: commonly the server’s payment challenge. Inspect its offered requirements.
- Another 402 after payment submission: may mean the payment was rejected. Read the x402 error details and response headers.
- 5xx response: points to a server-side processing problem in the transport mapping, but inspect the body and headers before concluding where it occurred.
- Payment settled but resource is absent from a catalog: investigate Bazaar declaration, payload echoing, validation, and indexing separately from payment success.
Check the payment challenge before signing
Decode the challenge and compare its requirements with what the client and facilitator support. A supported network by itself does not guarantee support for the particular scheme and protocol version offered.
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x402Versionand the offeredscheme.networkandasset.amountandpayTo.- Whether the client selected an option that the chosen facilitator supports.
The amount is in atomic units, not necessarily a human-readable token quantity. Do not interpret an integer amount as a token balance without accounting for the asset’s units. Check the target chain and route against the project’s repository and production-path guidance; do not assume the public x402.org facilitator is the default production route for mainnet EVM.
#1 Best Overall
Fix authorization and payload errors
Use a compatible, maintained x402 client SDK to construct payment authorization rather than assembling the payload by hand. A malformed payload, an altered challenge, or a mismatch between the challenge and payment can fail validation. Check the protocol version, supported scheme/network combination, amount, recipient, signature, and authorization validity window against the requirements. The Cloudflare Monetization Gateway x402 documentation, last updated 2026-09-30, also describes v2 headers, SDK payload creation, and origin validation.
For AWS AgentCore integrations specifically, AWS identifies errors such as X402 Payload for signing is invalid. and Payment instrument network is required. Its guidance is to copy the merchant’s payload unchanged into paymentInput.cryptoX402 and use a payment instrument on the network specified by the merchant payload. Those field names and validation details are AgentCore-specific; other clients may handle payloads differently. See AWS AgentCore payment troubleshooting.
Rank #2
- Used Book in Good Condition
Separate verification from settlement
Facilitators may expose verification and settlement as separate operations. For example, PayAI’s reference describes POST /verify as checking a signed payment against requirements without moving funds, and POST /settle as submitting settlement. Its GET /supported endpoint reports supported combinations, while /discovery/resources serves catalog discovery. These paths describe PayAI’s service, not universal x402 endpoints; consult the PayAI facilitator reference for its current behavior.
Common protocol error checks include insufficient balance, an invalid authorization time window, wrong amount or recipient, invalid signature, unsupported network or scheme, malformed requirements or payload, protocol-version mismatch, and transaction state. Match the error to the relevant input or stage rather than retrying unchanged payment data.
If settlement is pending
settlement_pending is non-terminal: a transaction may have been broadcast but not yet confirmed. Use the non-empty transaction hash and stated network to reconcile its on-chain status before deciding whether to retry. Sending a fresh payment immediately can risk duplicate payment if the first transaction later confirms. Follow the facilitator’s response and the standard error guidance in the x402 Specification v2.
Why a settled service may not appear in a Bazaar catalog
Settlement and catalog listing are separate outcomes. The x402 Bazaar documentation explains that catalog behavior, indexing latency, and discovery APIs are outside the scope of the x402 open-source repository. Facilitators or catalog operators can implement discovery independently, so a listing is not guaranteed across the x402 ecosystem.
For a Bazaar listing, check the full path described in the Bazaar extension documentation:
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- Echo it in the payment payload. The paying client must carry the Bazaar extension into the
PaymentPayloadprocessed at settlement. A server-side declaration alone is insufficient. - Validate the schema. Check required
info.input.typeand, when output is present,info.output.type. Use an absoluteresource.url; ensure eachacceptsentry has the expected stringassetand atomic-unitamount; and validate metadata and schema references. - Check reference constraints. Schema
$refand$idvalues must be same-document JSON Pointer fragments beginning with#; external references are rejected. - Allow for processing and query the right catalog. A
processingstatus can mean indexing is still underway. Query the relevant facilitator’s catalog if its API is available, then contact that catalog operator if the entry remains absent.
Choosing a facilitator or SDK for this integration
Confirm current support for the exact combination you need rather than relying on a provider’s general claim of x402 support. Availability can change, so check current documentation or a live support endpoint where provided.
Quick Recap
Best Value
| What to verify | Why it matters |
|---|---|
| Protocol version | The client, server, and facilitator must interoperate on the version in use. |
| Scheme and network pair | Network support alone may not mean that the offered scheme/network combination is supported. |
| Verification and settlement behavior | Determine what each operation validates or submits and how the service reports pending or terminal transaction states. |
| Production readiness for the target chain | Check the intended production route and network; do not assume a public facilitator is the right mainnet route. |
| Catalog and discovery features | Discovery behavior, indexing, and APIs depend on the facilitator or catalog operator. |
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