> ## Documentation Index > Fetch the complete documentation index at: https://docs.aropay.aro.media/llms.txt > Use this file to discover all available pages before exploring further. # Mail letter > Print and mail an `ESCROWED` letter through **Lob** and move it to `MAILED`. `standard` is USPS First Class; `tracked` adds USPS Certified for US destinations or Registered for international ones, and populates `mail.trackingNumber` and tracking events. `courier` is not offered (`400 delivery_method_unavailable`). Requires the claim origin fixed at creation to be `https:` (`400 claim_origin_not_public`); paper cannot be corrected later. The submission is idempotent: retrying after a timeout adopts the letter Lob already accepted instead of mailing a second copy. Provider failures leave the letter `ESCROWED` with the attempt recorded. With a Lob **test** key (`test_…`) letters are validated and priced but never printed or mailed; the letter reports `mail.testMode: true`. ## OpenAPI ````yaml /api-reference/openapi.yaml post /transfer/letter/{id}/mail openapi: 3.1.0 info: title: AroPay API version: 1.0.0 description: | The AroPay API for orchestrating sealed, private payments on public ledgers, built on the Aro Confidential Rails (Zama Protocol FHE). Two environments run the same API: Production on Ethereum Mainnet (`aropay.aro.media`, real funds) and the Sandbox on Sepolia (`dev.aropay.aro.media`, test funds and a faucet). Integrations built against the sandbox carry over unchanged; the faucet (`POST /fund`) is sandbox-only and returns 404 on production. Every response (except the flat Sandbox probes) uses the shared envelope: `{ "ok": true, "data": … }` on success and `{ "ok": false, "error": { "code", "message", "details?" } }` on failure. Amounts are decimal strings in human units (e.g. `"125.50"`). Write requests must send `Content-Type: application/json`. contact: name: Aro Media url: https://aro.media servers: - url: https://aropay.aro.media/api/v1 description: Production (Ethereum Mainnet) - url: https://dev.aropay.aro.media/api/v1 description: Sandbox (Sepolia) - url: http://aropay.localhost:3000/api/v1 description: Local development security: - apiKeyAuth: [] - sessionCookie: [] tags: - name: Auth description: Password, TOTP, and passkey login; session inspection and logout. - name: Profile & security description: Profile, password, two-factor authentication, and passkey management. x-group: Profile & security - name: API keys description: Programmatic credentials. Creation and revocation are session-only. - name: Wallets description: Custodial and external (watch-only) wallets. - name: Balances description: Balance triples and lightweight gas reads. - name: Money movement description: | Faucet funding, minting, transfers, and redemptions. All four are asynchronous: the request is validated and recorded, the response is `201` with the transaction in status `QUEUED` (`txHash: null`), and a background worker executes it. Poll `GET /transactions/{id}` until `status` is `CONFIRMED`, `SETTLED`, or `FAILED`. Execution failures surface as status `FAILED` with `errorCode` on the transaction, never as an HTTP error on the POST. - name: Aro Mail description: >- Letters of value: escrow cAROUSD, print or mail through Lob, and let the recipient claim by QR or code. - name: Transactions description: >- History, single-transaction reads (pure database reads), and notarized receipts. - name: Sandbox description: Unauthenticated status and echo probes with a flat response shape. paths: /transfer/letter/{id}/mail: post: tags: - Aro Mail summary: Mail letter description: | Print and mail an `ESCROWED` letter through **Lob** and move it to `MAILED`. `standard` is USPS First Class; `tracked` adds USPS Certified for US destinations or Registered for international ones, and populates `mail.trackingNumber` and tracking events. `courier` is not offered (`400 delivery_method_unavailable`). Requires the claim origin fixed at creation to be `https:` (`400 claim_origin_not_public`); paper cannot be corrected later. The submission is idempotent: retrying after a timeout adopts the letter Lob already accepted instead of mailing a second copy. Provider failures leave the letter `ESCROWED` with the attempt recorded. With a Lob **test** key (`test_…`) letters are validated and priced but never printed or mailed; the letter reports `mail.testMode: true`. operationId: mailLetter parameters: - $ref: '#/components/parameters/LetterId' requestBody: required: true content: application/json: schema: $ref: '#/components/schemas/MailLetterRequest' example: deliveryMethod: tracked provider: lob responses: '200': description: The letter as `MAILED`, with `mail` populated. content: application/json: schema: $ref: '#/components/schemas/LetterEnvelope' example: ok: true data: letter: id: cklet0001abcd status: MAILED chainId: 11155111 amount: '50.00' token: cAROUSD amountVisibility: sealed memo: Thanks for the referral recipient: name: Jane Doe address: line1: 12 Adeola Odeku Street line2: Victoria Island landmark: Opposite Eko Hotel city: Lagos region: LA postal: null country: NG countryName: Nigeria isDomestic: false expiresAt: '2026-10-22T09:45:00.000Z' sender: walletId: ckwlt0001abcd address: '0x8Ba1f109551bD432803012645Ac136ddd64DBA72' claimCode: 7K3M-Q9TX-2ABF-H8RD-5CWN-VGP4-0J6Y claimUrl: >- https://dev.aropay.aro.media/claim#7K3M-Q9TX-2ABF-H8RD-5CWN-VGP4-0J6Y pdfUrl: >- https://dev.aropay.aro.media/api/v1/transfer/letter/cklet0001abcd/pdf escrow: transactionId: cktxn0005abcd txHash: 0x4d1e… explorerUrl: https://sepolia.etherscan.io/tx/0x4d1e… status: CONFIRMED verified: true claim: null refund: null mail: provider: lob providerId: ltr_4868c3b5655f1f5c deliveryMethod: tracked status: processed trackingNumber: '9407300000000000000004' expectedDeliveryDate: '2026-09-22' mailedAt: '2026-09-07T10:02:11.000Z' testMode: true needsReview: false error: null createdAt: '2026-09-07T09:45:00.000Z' updatedAt: '2026-09-07T10:02:11.000Z' '400': description: > Letter not `ESCROWED` (`letter_not_escrowed`, `letter_already_mailed`), `deliveryMethod: "courier"` (`delivery_method_unavailable`), a non-`https:` claim origin (`claim_origin_not_public`), Lob rejecting the address (`invalid_postal_address`), or validation. content: application/json: schema: $ref: '#/components/schemas/ErrorResponse' example: ok: false error: code: letter_already_mailed message: This letter has already been mailed. '401': $ref: '#/components/responses/Unauthorized' '402': description: >- Lob could not accept the letter (outage, timeout, or a non-address rejection). The letter stays `ESCROWED`. content: application/json: schema: $ref: '#/components/schemas/ErrorResponse' example: ok: false error: code: postage_unavailable message: >- Lob rejected the letter: file must be a PDF with 8.5x11 inch pages. '403': $ref: '#/components/responses/AccountDisabled' '404': $ref: '#/components/responses/LetterNotFound' '429': $ref: '#/components/responses/RateLimited' '500': $ref: '#/components/responses/InternalError' '503': description: >- Lob is not configured on this deployment (missing or rejected `LOB_API_KEY`, or incomplete return address). content: application/json: schema: $ref: '#/components/schemas/ErrorResponse' example: ok: false error: code: mail_provider_not_configured message: Mailing is not configured on this deployment. components: parameters: LetterId: name: id in: path required: true schema: type: string description: Letter ID. schemas: MailLetterRequest: type: object required: - deliveryMethod properties: deliveryMethod: type: string enum: - standard - tracked - courier description: > `standard`: USPS First Class. `tracked`: First Class plus USPS Certified (US) or Registered (international), with tracking. `courier` is not offered and returns `400 delivery_method_unavailable`. provider: type: string enum: - lob description: Optional; `lob` is the only provider. LetterEnvelope: type: object required: - ok - data properties: ok: const: true data: type: object required: - letter properties: letter: $ref: '#/components/schemas/Letter' ErrorResponse: type: object description: The shared failure envelope. required: - ok - error properties: ok: const: false error: type: object required: - code - message properties: code: type: string description: Machine-readable error code; match on this, not `message`. message: type: string details: description: Structured context, e.g. per-field validation issues. Letter: type: object description: | An Aro Mail letter: escrowed cAROUSD, a recipient address, a one-time claim code, and the legs that moved value. required: - id - status - chainId - amount - token - amountVisibility - memo - recipient - isDomestic - expiresAt - sender - claimCode - claimUrl - pdfUrl - escrow - claim - refund - mail - needsReview - error - createdAt - updatedAt properties: id: type: string examples: - cklet0001abcd status: type: string enum: - DRAFT - ESCROWED - MAILED - CLAIMING - CLAIMED - EXPIRED - VOIDED - FAILED description: | `DRAFT` (escrow submitted) → `ESCROWED` (escrow verified) → optional `MAILED` → `CLAIMING` → `CLAIMED`. `EXPIRED` and `VOIDED` carry a refund leg. `FAILED` means the escrow reverted, clamped or was never submitted: no value left the sender. Claimable: `ESCROWED`, `MAILED`. Terminal: `CLAIMED`, `EXPIRED`, `VOIDED`, `FAILED`. chainId: type: integer examples: - 11155111 amount: type: string description: >- Decimal string in human units. Cleartext to the parties; encrypted on-chain. token: type: string examples: - cAROUSD amountVisibility: type: string enum: - sealed - visible description: >- Whether the printed letter shows the amount. Defaults to `visible` domestic, `sealed` international. memo: type: - string - 'null' description: Up to 200 characters, printed on the letter. recipient: type: object required: - name - address properties: name: type: string address: $ref: '#/components/schemas/LetterAddress' isDomestic: type: boolean description: >- True when the destination is the deployment's home country (`US` by default). expiresAt: type: string format: date-time sender: type: object required: - walletId - address properties: walletId: type: - string - 'null' description: >- The sending wallet; `null` if that wallet was later deleted (refunds still go to `address`). address: type: string description: EIP-55 address the escrow came from and refunds return to. claimCode: type: - string - 'null' description: | Display form (`XXXX-XXXX-XXXX-XXXX-XXXX-XXXX-XXXX`, 28 Crockford base32 symbols incl. two check symbols). Owner-only: present on create and single reads while the letter is non-terminal; `null` in lists and once terminal. claimUrl: type: - string - 'null' description: >- `https:///claim#`; the QR payload. Same visibility as `claimCode`. pdfUrl: type: string description: >- Absolute URL of `GET /transfer/letter/{id}/pdf`, built from the claim origin fixed at creation. escrow: description: >- The `LETTER_ESCROW` leg (sender → vault); `null` only if the row was never created. oneOf: - $ref: '#/components/schemas/LetterLeg' - type: 'null' claim: description: >- The `LETTER_CLAIM` leg (vault → recipient wallet); `null` until someone claims. oneOf: - allOf: - $ref: '#/components/schemas/LetterLeg' - type: object required: - claimedAt - walletAddress properties: claimedAt: type: - string - 'null' format: date-time description: Set when the letter reaches `CLAIMED`. walletAddress: type: - string - 'null' description: The wallet the value was released to. - type: 'null' refund: description: >- The `LETTER_REFUND` leg (vault → sender address); `null` unless the letter was voided or expired. oneOf: - allOf: - $ref: '#/components/schemas/LetterLeg' - type: object required: - reason properties: reason: type: string enum: - voided - expired - type: 'null' mail: description: >- Fulfilment details; `null` until `POST /transfer/letter/{id}/mail` is attempted. oneOf: - type: object required: - provider - providerId - deliveryMethod - status - trackingNumber - expectedDeliveryDate - mailedAt - testMode properties: provider: type: string examples: - lob providerId: type: - string - 'null' description: Lob letter id once accepted. deliveryMethod: type: - string - 'null' enum: - standard - tracked - courier - null status: type: - string - 'null' description: >- Lob letter status (`processed`, `rendered`, `failed`), refreshed on owner reads. trackingNumber: type: - string - 'null' description: >- USPS tracking number for `tracked` letters (dummy in test mode). expectedDeliveryDate: type: - string - 'null' description: Lob's estimate, `YYYY-MM-DD`. mailedAt: type: - string - 'null' format: date-time testMode: type: boolean description: >- True when the deployment uses a Lob test key; nothing is printed or mailed. - type: 'null' needsReview: type: boolean description: >- True when a leg could not be verified automatically; nothing moves until an operator reviews `error`. error: type: - string - 'null' description: Failure or review context for the most recent leg. createdAt: type: string format: date-time updatedAt: type: string format: date-time LetterAddress: type: object description: Recipient postal address as stored, with the resolved country name. required: - line1 - line2 - landmark - city - region - postal - country - countryName properties: line1: type: string line2: type: - string - 'null' landmark: type: - string - 'null' description: Printed as `Near …` on the letter. city: type: string region: type: - string - 'null' postal: type: - string - 'null' country: type: string description: ISO 3166-1 alpha-2, upper-case. examples: - NG countryName: type: string examples: - Nigeria LetterLeg: type: object description: >- One on-chain leg of a letter (escrow, release or refund), linked to its transaction row. required: - transactionId - txHash - explorerUrl - status - verified properties: transactionId: type: string description: The `Transaction` id; read it with `GET /transactions/{id}`. examples: - cktxn0005abcd txHash: type: - string - 'null' explorerUrl: type: - string - 'null' status: type: string enum: - PENDING - CONFIRMED - SETTLING - SETTLED - FAILED description: The linked transaction's status. verified: type: boolean description: | True once the leg's `ConfidentialTransfer` event was decrypted and matched the letter amount. The letter only changes status after verification, so `CONFIRMED` + `verified: false` means the receipt is in and verification is pending. responses: Unauthorized: description: Missing or invalid credential. content: application/json: schema: $ref: '#/components/schemas/ErrorResponse' example: ok: false error: code: invalid_api_key message: Invalid API key. AccountDisabled: description: The account has been deactivated. content: application/json: schema: $ref: '#/components/schemas/ErrorResponse' example: ok: false error: code: account_disabled message: This account is disabled. LetterNotFound: description: >- No letter with this id in your account (or no letter matches the claim code). content: application/json: schema: $ref: '#/components/schemas/ErrorResponse' example: ok: false error: code: letter_not_found message: Letter not found. RateLimited: description: Rate limit exceeded. content: application/json: schema: $ref: '#/components/schemas/ErrorResponse' example: ok: false error: code: rate_limited message: Too many requests. Try again shortly. InternalError: description: Unexpected server error. content: application/json: schema: $ref: '#/components/schemas/ErrorResponse' example: ok: false error: code: internal_error message: An unexpected error occurred. securitySchemes: apiKeyAuth: type: http scheme: bearer bearerFormat: aro_sk_… description: | AroPay API key, sent as `Authorization: Bearer aro_sk_…`. Created in the dashboard under Settings → API keys. Takes precedence over a session cookie when both are present. x-default: aro_sk_your_key_here sessionCookie: type: apiKey in: cookie name: aropay_session description: | Browser session cookie minted by `POST /auth/login` (or passkey login). httpOnly, `SameSite=Lax`, 24 h TTL. Endpoints marked **Session-only** accept only this credential and return `403 session_required` for API keys. ````