> ## Documentation Index > Fetch the complete documentation index at: https://docs.dripstack.com/llms.txt > Use this file to discover all available pages before exploring further. # Payment Flow > Wallet payment challenges, API-key credits, headers, and pricing semantics. Paid article-summary routes support two payment models: * **Payment-aware clients** use x402 with USDC on Base or Solana, or MPP on Tempo or Stripe (card / Link). A plain request returns HTTP `402`, then the client retries with payment credentials. * **API-key clients** authenticate with [`Authorization: Bearer pk_drip_...`](/quickstart-api-keys) and spend account credits. API keys do not use the 402 wallet handshake. Each first successful paid fetch of a post summary unlocks that post forever for the paying subject. Later fetches of the same post return the live summary with no charge and no new sale. Credits / API key / JWT / MCP OAuth share the same Drip-user entitlement (including in-app chat paid fetches). x402 and MPP clients should store `X-Drip-Unlock` / `unlockToken` from the first settle and send it on free re-reads. If the token is lost but the same wallet (x402) or validated MPP credential is presented again, the server detects the existing unlock, skips the charge, and re-issues a token. ### Response fields | Situation | `paymentInfo.protocol` | `amountUsd` | `unlocked` | `unlockToken` / `X-Drip-Unlock` | | - | - | - | - | - | | First x402 / MPP pay | `x402` / `mpp` | charged price | omitted | issued | | Free re-read via `X-Drip-Unlock` | `unlock` | `"0.00"` | `true` | omitted (client already has it) | | Free re-read via same wallet / validated MPP (lost token) | `unlock` | `"0.00"` | `true` | re-issued | | First credits pay | `mpp` or `credits` | charged price | omitted | never | | Credits free re-read | `unlock` | `"0.00"` | `true` | never | A first API-key post response can report `protocol: "mpp"` when Drip completes the credit-funded payment through MPP, or `"credits"` otherwise. The request still spends the authenticated user's credits. Use the credit ledger to inspect the debit; `spendSource` is not a response field. Lifetime unlocks apply only to individual posts. Paid stock-picks bundles are charged on each request and do not grant access to their source posts. Stock Picks V2 also offers subscription access; see [Stock Picks](/stock-picks). Invalid or revoked `X-Drip-Unlock` does not block payment: when a pay credential is also present, the request falls through to that rail (or to a `402` challenge if none). ## The 402 handshake for wallet clients 1. A plain request to a paid route returns `402` with two headers: * `WWW-Authenticate: Payment ...` — the MPP challenges for Tempo and Stripe * `PAYMENT-REQUIRED` — the x402 v2 challenge 2. Retry the **same request** through a payment-aware client, or manually with: * `Authorization: Payment ` for MPP, or * a `PAYMENT-SIGNATURE` header for x402 v2. 3. On success (`200`), the response includes `synthesizedSummary` and `paymentInfo`. The `402` response lets a wallet-aware client inspect the exact runtime price before authorizing payment. For discovery-time estimates, publication post listings include `priceCents`. The runtime challenge is authoritative. Treat a `402` as a "pay and retry" signal, not a failure. If a plain HTTP request returns `402`, retry it through the payment-aware client rather than surfacing an error. A plain request returns a challenge rather than the paid summary: ```http theme={null} HTTP/1.1 402 Payment Required PAYMENT-REQUIRED: WWW-Authenticate: Payment ``` After a successful payment, the response identifies how the request was paid: ```json theme={null} { "publicationSlug": "fabricatedknowledge.com", "slug": "ais-600b-question", "title": "AI's $600B Question", "synthesizedSummary": "The article examines whether projected AI revenue can justify rapidly expanding infrastructure spending...", "paymentInfo": { "amountUsd": "0.50", "protocol": "x402" } } ``` ## API-key credits API keys are traditional bearer tokens created from the [API keys page](https://dripstack.com/connect/api). Use them when your agent or backend service should spend an account balance instead of holding a wallet. ```bash theme={null} curl \ "https://dripstack.com/api/v1/publications/fabricatedknowledge.com/ais-600b-question" \ -H "Authorization: Bearer $DRIP_API_KEY" ``` API keys spend available account credits, using signup credits before top-ups for signed-in accounts. If the balance is too low, the paid route returns `403` with `reason: "insufficient_credits"` instead of issuing a 402 payment challenge. See the [API-key quickstart](/quickstart-api-keys) for the full setup and request examples. ## Inspect pricing before payment List a publication's recent posts to compare prices before selecting one: ```bash theme={null} curl "https://dripstack.com/api/v1/publications/fabricatedknowledge.com?limit=5" ``` ```json theme={null} { "posts": [ { "slug": "ais-600b-question", "title": "AI's $600B Question", "publishedAt": "2026-06-14T12:00:00.000Z", "priceCents": 50 } ] } ``` `priceCents` is useful for selection and agent spending limits. When requesting the paid route with a wallet, inspect the returned `402` challenge before authorizing payment because it contains the live price. ## Discovery pricing vs runtime pricing The OpenAPI discovery document exposes `x-payment-info.offers[]` on paid routes. These offers are **advisory** — they may list Base or Solana USDC (x402), Tempo, and Stripe charges, or catalog floor prices. The **runtime `402` challenge is authoritative**. Per-post pricing comes from the live challenge, and the price may scale with content — for example, stock-picks charge a flat unit price times the number of distinct attributed source articles in the response. Always trust the live `402` over publication listings or discovery offers. ## Status codes | Status | Meaning | Action | | - | - | - | | `200` | Summary returned; charged on first unlock | Read `synthesizedSummary` | | `402` | Payment required | Retry the same request through a payment-aware client | | `403` | Insufficient account credits (API keys) | Top up the credit balance | | `404` | Content not found | Do not pay; verify the publication / post slugs | | `503` | Summary not ready (`summary_not_ready`) | Retry later; no payment challenge is issued | A `404` and a `503` never carry a payment challenge — do not pay on either. `503` means the summary is still being generated; retry shortly. For production handling, see [Errors & Retries](/concepts/errors-retries). ## Discovery Prefer `GET /openapi.json` (OpenAPI 3.1) for route shapes, JSON schemas, and paid-route `x-payment-info.offers[]` metadata. If OpenAPI is unavailable, use `GET /.well-known/x402` for the paid resource list in `METHOD /path` form. The root `x-discovery.ownershipProofs` field is a Drip vendor extension, not part of core MPP discovery. This documentation is built and hosted on [Mintlify](https://mintlify.com), a developer documentation platform.