> ## Documentation Index > Fetch the complete documentation index at: https://mintfax.com/docs/llms.txt > Use this file to discover all available pages before exploring further. # Send a Fax > Submit a fax for delivery. The file is staged and the fax is queued for processing. A credit hold is placed on submission and captured on delivery or released on failure. ## OpenAPI ````yaml /openapi.json post /faxes openapi: 3.1.0 info: title: mintfax API version: '1.0' description: >- Developer-first fax API. Send faxes with a single API call. ## Authentication Most endpoints require a Bearer token in the `Authorization` header. - **Account keys** (`mfx_acct_...`) access account-level endpoints (`/account`, `/account/balance`, `/account/transactions`, `/account/keys`). - **Environment keys** (`mfx_test_...` for test, `mfx_live_...` for live) access operational endpoints (`/environment`, `/faxes`, `/webhooks`, `/events`). - Registration endpoints (`POST /account/register` and `POST /account/register/verify`) do not require authentication. ## Base URL All API requests use `https://api.mintfax.com/v1` as the base URL. contact: name: mintfax Support email: support@mintfax.com url: https://mintfax.com/docs servers: - url: https://api.mintfax.com/v1 description: Production security: - bearerAuth: [] tags: - name: Account description: >- Account-level resources: registration, account info, balances, and API keys. - name: Environment description: >- Test and live environment configuration shared across all operational requests. - name: Fax description: Send, list, retrieve, resend, and purge faxes. - name: Events description: >- Read the immutable event log for everything that has happened in the environment. - name: Webhooks description: >- Manage webhook endpoints and inspect or replay individual delivery attempts. paths: /faxes: post: tags: - Fax summary: Send a Fax description: >- Submit a fax for delivery. The file is staged and the fax is queued for processing. A credit hold is placed on submission and captured on delivery or released on failure. operationId: sendFax parameters: - name: Idempotency-Key in: header description: >- Client-generated key for idempotent submission (recommended). Duplicate keys return the original response without re-processing. Keys expire after 24 hours. schema: type: string example: order-1234-attempt-1 requestBody: required: true content: multipart/form-data: schema: $ref: '#/components/schemas/SubmitFaxRequest' responses: '201': description: '`FaxSubmissionResource`' content: application/json: schema: $ref: '#/components/schemas/FaxSubmissionResource' headers: X-Idempotency-Key: description: >- Echoed back when the request supplied an `Idempotency-Key` header. Absent when the client omitted the request header. required: false schema: type: string example: order-1234-attempt-1 Idempotency-Replayed: description: >- Set to `true` when this response was served from the idempotency cache rather than re-processing the request. Absent (not `false`) when the response represents a freshly processed submission. required: false schema: type: string example: 'true' '401': description: The provided API key is not recognised. content: application/json: schema: $ref: '#/components/schemas/Error' examples: api_key_invalid: value: error: api_key_invalid message: The provided API key is not recognised. action: check_credentials docs: https://mintfax.com/docs/errors/api-key-invalid '402': description: Insufficient balance for this operation. content: application/json: schema: $ref: '#/components/schemas/Error' examples: insufficient_balance: value: error: insufficient_balance message: Insufficient balance for this operation. action: top_up_balance docs: https://mintfax.com/docs/errors/insufficient-balance context: available: 50 required: 100 '403': description: >- Live calls require account activation. Complete a first credit purchase to activate. content: application/json: schema: $ref: '#/components/schemas/Error' examples: account_not_activated: value: error: account_not_activated message: >- Live calls require account activation. Complete a first credit purchase to activate. action: activate_account docs: https://mintfax.com/docs/errors/account-not-activated key_not_scoped_for_operations: value: error: key_not_scoped_for_operations message: >- This API key cannot send faxes or read environment data. Use an mfx_test_ or mfx_live_ key. action: use_operational_key docs: >- https://mintfax.com/docs/errors/key-not-scoped-for-operations '422': description: The request failed validation. content: application/json: schema: $ref: '#/components/schemas/Error' examples: validation_failed: value: error: validation_failed message: The request failed validation. action: fix_request docs: https://mintfax.com/docs/errors/validation-failed context: errors: to: - The to field is required. file: - The file field is required. '500': description: >- An unexpected error occurred. Please retry; if the problem persists, contact support. content: application/json: schema: $ref: '#/components/schemas/Error' examples: internal_server_error: value: error: internal_server_error message: >- An unexpected error occurred. Please retry; if the problem persists, contact support. action: retry_or_contact_support docs: https://mintfax.com/docs/errors/internal-server-error components: schemas: SubmitFaxRequest: type: object properties: to: type: string pattern: ^\+[1-9]\d{1,14}$ file: type: string format: binary contentMediaType: application/octet-stream maxLength: 10240 webhook_url: type: - string - 'null' format: uri maxLength: 2048 max_attempts: type: - integer - 'null' minimum: 1 maximum: 5 csid: type: - string - 'null' maxLength: 20 page_size: type: - string - 'null' enum: - letter - legal - a4 - b4 resolution: type: - string - 'null' enum: - standard - fine optimize_for: type: - string - 'null' enum: - text - photo tags: type: - array - 'null' items: type: string maxLength: 255 maxItems: 10 required: - to - file title: SubmitFaxRequest FaxSubmissionResource: type: object properties: id: type: string description: Unique fax identifier (fax_-prefixed). examples: - fax_8aZqRm4yT3vK7pNxJ2bH9c status: $ref: '#/components/schemas/FaxStatus' description: Initial fax status. examples: - queued to: type: - string - 'null' description: Destination fax number in E.164 format. examples: - '+12125551234' tags: type: object description: Echo of caller-supplied metadata. Empty serializes as `{}`. additionalProperties: type: string created_at: type: string format: date-time description: UTC timestamp when the fax record was created. resent_from: type: string description: >- Original fax identifier when this submission is a resend; only present on resends. examples: - fax_8aZqRm4yT3vK7pNxJ2bH9c required: - id - status - to - tags - created_at title: FaxSubmissionResource Error: type: object properties: error: type: string description: Machine-readable error code. example: insufficient_balance message: type: string description: Human-readable description. example: Insufficient balance for this operation. action: type: string description: Suggested next step for the caller. example: top_up_balance docs: type: string format: uri description: URL to the docs entry for this error code. example: https://mintfax.com/docs/errors/insufficient-balance request_id: type: string description: >- Unique identifier for this API request, also returned in the X-Request-Id response header. Include this value in support requests for fast triage. pattern: ^req_[0-9A-HJKMNP-TV-Z]{26}$ example: req_01J9XYZQ8KH7B3R0WXAZP8VW6F context: type: object description: Error-specific extra fields (e.g. balances, validation errors). additionalProperties: [] required: - error - message - action - docs - request_id title: Error FaxStatus: type: string enum: - queued - submitted - in_progress - delivered - failed title: FaxStatus securitySchemes: bearerAuth: type: http description: |- API key as Bearer token. Use an account key (`mfx_acct_...`) for `/account/*` endpoints, and an environment key (`mfx_test_...` for sandbox, `mfx_live_...` for live) for `/environment/*`, `/faxes`, `/webhooks`, and `/events`. scheme: bearer ````