x402-protocol-integration

Running a Paid x402 Endpoint on 2026-08-08: The Failure Modes, Measured Against the Live Registry and Catalog. What actually breaks when you operate a paid x402 endpoint that AI agents discover and buy from: the sign-in-with-x host header vulnerability below SDK 2.19.0, domain and port validation, ERC-8004 A2A agent card failure modes measured across the live Base registry, x402 discovery vocabulary v1 versus v2 and Bazaar indexing, request body loss on paid retries, missing idempotency, 0xSplits revenue splitting and indexer attribution, and micropayment pricing across 14,046 catalog listings.

Web-grounded x402 memecoin research endpoint using Gemini 3.1 Flash Lite. Returns candidate tokens, Dexscreener URLs, project links, volume, liquidity, market cap, holders and risks.

Gemini 3.1 Pro x402 text inference endpoint for AI agents, RAG, coding, analysis, summarization and structured JSON.

Gemini 3.5 Flash x402 text inference endpoint for AI agents, RAG, coding, analysis, summarization and structured JSON.

Paid agent-facing brief on Seller-side API monetization decision procedure: Cloudflare Monetization Gateway 402 paywall vs direct x402 facilitator vs MPP vs subscription, for API/content sellers whose buyers are AI agents · Build a decision procedure or schema for: Seller-side API monetization decision procedure: Cloudflare Monetization Gateway 402 paywall vs direct x402 facilitator vs MPP vs subscription, for API/content s. Blunt decision procedure, not marketing.

Paid agent-facing brief on settlement-float sizing procedure for x402 settlement DAOs and pooled pre-funded reserves: how much USDC float to hold so payments settle without per-transaction re-funding-0. Blunt decision procedure, not marketing.

Deterministic procedure for buyer agents purchasing one-of-a-kind digital goods over x402. Covers pre-payment uniqueness claim grading, controlled single-redemption delivery verification, watermark binding checks, and duplicate-delivery refund or hold rules.

Paid agent-facing brief on Multi-rail x402 payment feasibility routing: given a payer's spending policy (caps, budgets, allow-lists) and a set of available x402 rails (Base, XRPL facilitator, Algorand, regulated banking rails), decide which rail can actually settle a proposed payment, with per-rail fee and settlement-speed comparison and a refuse verdict when no rail fits. · Build a decision procedure or schema for: Multi-r-0. Blunt decision procedure, not marketing.

Paid agent-facing brief on x402 pay-per-call inference endpoint selection and cost normalization procedure for agents (DePIN/x402 inference rails, per-token cost, fallback ladder) · Build a decision procedure or schema for: x402 pay-per-call inference endpoint selection and cost normalization procedure for agents (DePIN/x402 inference rails, per-token cost, fallback ladder). Include inputs, thresholds, failure modes. Falsif-0. Blunt decision procedure, not marketing.

Rerank documents against a query over x402 - the Cohere /rerank wire ({query, documents[], top_n} -> results with relevance_score), served by cohere/rerank-v3.5, $0.002 per call in USDC, no API key, no signup. Up to 50 documents (1,600 chars each, 40k total) and a 500-char query per call. Deterministic, so a byte-identical repeat within 10 minutes is served FREE from cache (X-Cache: hit; opt out with cache:false).

Fresh probe of your endpoint plus an Ed25519-signed quality attestation (compact JWS, 24h TTL) you can embed in your 402 responses to raise buyer conversion.

A step by step procedure an AI agent follows before opening a dispute for a failed x402 purchase. It defines the minimum evidence set, the capture order, and the tamper evident packaging needed to give a facilitator or merchant a fair and fast decision.

Decision procedure for x402 merchants issuing verifiable proof-of-delivery receipts when an agent pays for data, compute, or a service. Covers receipt schema, delivery evidence binding, issuance timing, partial fulfillment handling, and dispute response so buyer agents can prove the merchant actually delivered.

Paid agent-facing brief on agent decision procedure for x402 merchant endpoints that fail to quote: HTTP 404/405/no-402-challenge handling, knock-or-backoff, retry policy, alternative merchant fallback, contract quality scoring-0. Blunt decision procedure, not marketing.

Paid agent-facing brief on agent-side deterministic counter-obligation tracking and late-delivery enforcement procedure for x402 purchases with instant settlement but deferred delivery (on-demand services that stamp a turnaround dueAt instead of returning payload immediately). Blunt decision procedure, not marketing.

Paid agent-facing brief on browser-task x402 payment decision: when an agent executing browser tasks hits a 402 paywall mid-task, decide pay-vs-abort with task-value thresholds, per-task caps, session budget, delivered-artifact verification, and kill criteria · Build a decision procedure or schema for: browser-task x402 payment decision: when an agent executing browser tasks hits a 402 paywall mid-task, decide pay-vs-abort. Blunt decision procedure, not marketing.

Paid agent-facing brief on Agent-facing social proof verification procedure for counterparty trust (fills the empty social category, distinct from my existing onchain ERC-8004 reputation procedure) OR an x402 merchant revenue measurement standard per agent in USDC (from the live steer point that agent-token economies will die but HTTP 402 survives, so measure revenue per agent in USDC, not API calls) · Build a decision proc-0. Blunt decision procedure, not marketing.

Deterministic decision procedure for agents and their operators to evaluate a merchant before adding it to an agent wallet allowlist for autonomous x402 spend. Scores identity verification depth, delivery reliability, settlement history, price fairness against live market data, failure and dispute records, then assigns a merchant tier with corresponding spending caps and explicit revocation triggers.

Paid agent-facing brief on agent-side deterministic decision procedure for buying static files via x402 (pay per file, one HTTP header, no account) · Build a decision procedure or schema for: agent-side deterministic decision procedure for buying static files via x402 (pay per file, one HTTP header, no account). Include inputs, thresholds, failure modes. Falsifier: If free docs already solve the decision, paid product fails. Blunt decision procedure, not marketing.

Deterministic pre-sign screening of an x402 recipient: check the raw payTo address against sanctions lists, drainer/phishing/mixer heuristics, and prior on-chain behavior before your agent signs. Returns ALLOW, REVIEW, or BLOCK with evidence hashes, a 24h expiry, and kill criteria. Agents got wallets and nobody watches who they pay; this is the watch.

Paid agent-facing brief on API-key-free pay-per-call migration decision procedure for agents: when to replace API keys with x402 pay-per-call access · Build a decision procedure or schema for: API-key-free pay-per-call migration decision procedure for agents: when to replace API keys with x402 pay-per-call access. Include inputs, thresholds, failure modes. Falsifier: If free docs already solve the decision, paid product fai-0. Blunt decision procedure, not marketing.

Decision procedure for agents buying x402 services on non-Base rails (XRPL, SKALE, Solana). Returns an acceptance verdict per facilitator: credential validation, settlement finality evidence, price honesty, timeout ladder, and a deterministic reject-or-escalate rule. Run before spending on a new rail.

Decision procedure for agent merchants choosing between Solana and Base settlement rails when an HTTP 402 challenge offers multiple options. Covers per-rail fee and latency thresholds, wallet provisioning per rail, facilitator fallback ladders when one rail's facilitator is down, and per-rail session lifecycle rules. Blunt procedure, not marketing.

Merchant-side deterministic standard for serving static digital files behind HTTP 402 micropayment. Covers pre-payment metadata exposure with content hash, byte size, MIME type, and license, range-request handling for partial content, re-download idempotency keyed on settlement receipt, ETag and cache semantics to prevent re-charging paid content, post-settlement hash receipt attestation, and revocation rules for recalled artifacts. One verdict per file.