{"uid":"cap_UVMDANMVXOO0J2lk6dgw-","slug":"the402-thread-message-sender-924aa104","name":"the402 — Post Message to Thread","description":"The open marketplace where AI agents discover and purchase services via x402 micropayments (USDC on Base L2). Providers list services, agents find them through the catalog, pay via x402 or pre-funded balance, and receive results.","url":"https://api.the402.ai/v1/threads/%7Bid%7D/messages","method":"POST","headers":{},"bodySchema":null,"responseSchema":{"type":"object"},"example":null,"exampleRequest":null,"tags":["x402"],"displayCostAmount":"0.001","displayCostAsset":"USDC","priceDynamic":false,"priceHint":null,"priceStatus":"priced","priceSource":"probe","requiresHandshake":false,"reviewCount":0,"rating":{"score":"0.00","successRate":"0.00","reviews":0,"stars":null,"state":"unrated"},"availabilityStatus":"down","priceObserved":null,"sessionDeposit":null,"pricing":{"kind":"static","summary":"$0.001/call","primary":{"kind":"static","protocol":"x402","network":"base","amountUsd":"0.001","per":"call","confidence":"exact"},"accepted":[{"kind":"static","protocol":"x402","network":"base","amountUsd":"0.001","per":"call","confidence":"exact"}]},"paymentMethods":[{"uid":"pm_mLb3ku34cLguENnzBM5rT","protocol":"x402","methodType":"crypto","chain":"base","mode":"charge","costAmount":"0.001","costPer":"request","priority":0,"asset":"0x833589fCD6eDb6E08f4c7C32D4f71b54bdA02913","unit":"request","depositMicros":null,"planRef":null}],"brandName":null,"brandSlug":null,"brandBaseUrl":null,"brandDocsUrl":null,"whatItDoes":"Posts a new message to a specific conversation thread on the the402.ai agent service platform.","exampleAgentPrompt":"Add a follow-up message to thread abc123 on the402 saying 'Please summarize the extracted document in bullet points' so the agent continues processing from where we left off.","exampleUseCases":[{"title":"Resume multi-step document review workflow","prompt":"Post a message to our thread on the402 asking the agent to validate the data extraction results from the previous step before we proceed to the next batch of documents."},{"title":"Inject real-time user feedback into agent loop","prompt":"Send a correction message to the active agent thread telling it that the extracted customer information was wrong and to re-parse the document with stricter validation rules."},{"title":"Escalate task to specialized agent mid-session","prompt":"Add a message to the current thread instructing the agent to hand off this complex case to our specialized legal review agent and include all the context from our conversation so far."}],"resultDescription":"Returns a message object confirming the message was posted to the thread, including the new message ID, timestamp, role, and content as stored in the thread.","failureModes":["Thread ID not found — 404 if the thread does not exist or has expired","Invalid message body — 400 if required fields like content or role are missing","Authentication failure — 401 if the x402 payment or API credentials are invalid","Payment insufficient — 402 if the caller's balance is below the $0.001 USDC per-call fee","Malformed request body — 400 if JSON is invalid or schema is incorrect","Thread already closed — 409 if the thread is in a terminal state and no longer accepts messages"],"whenToPreferThis":"Use this endpoint when you need to append a message to an existing the402.ai conversation thread — for example, continuing a multi-turn agent session, sending a follow-up instruction, or injecting a user reply into an ongoing workflow. Prefer this over starting a new thread when you already have a thread ID from a prior session.","instructions":null,"reviewSummary":null,"reviewSummaryHighlights":null,"reviewSummaryConcerns":null,"reviewSummaryGeneratedAt":null,"activationCount":0,"lastUsedAt":null,"lastSuccessfullyRanAt":null,"lastHealthCheckAt":"2026-09-15T20:25:34.358Z","isFirstParty":false}