Nixflex - AI Voice Platform for Building AI Phone Agents

The Nixflex API is REST over HTTPS. All requests use JSON. Authentication is via Bearer token (see Authentication).

Base URL

https://api.nixflex.com

All endpoints in this reference are relative to this base URL.

Versioning

The current version is v1. All paths are prefixed /v1/. When v2 is released, v1 will continue working unchanged for at least 12 months. Breaking changes always live behind a new version.

Authentication

Every request requires an Authorization header:

Authorization: Bearer key_id:key_secret

The colon between key_id and key_secret is required. See Authentication for details.

Request format

POST, PUT, and PATCH requests must include Content-Type: application/json and a JSON body. GET requests use query parameters where applicable.

Response format

All responses are JSON. Success responses return the resource directly:

{
  "agent_id": "agent_125207e452f8714a",
  "name": "Test Receptionist",
  ...
}

Error responses follow a consistent envelope (see Errors):

{
  "error": {
    "type": "invalid_request",
    "code": "invalid_phone_format",
    "message": "..."
  }
}

Result limits

Nixflex does not currently support offset-based pagination. Each list endpoint returns a fixed set of results:

Endpoint	Returns	`limit` supported
`GET /v1/calls`	The 50 most recent calls	No
`GET /v1/agents`	All active agents	No
`GET /v1/phone-numbers`	All numbers (up to 1,000)	No
`GET /v1/campaigns`	All campaigns	Yes
`GET /v1/sms/campaigns`	All campaigns	Yes

curl "https://api.nixflex.com/v1/campaigns?limit=10" \
  -H "Authorization: Bearer KEY_ID:KEY_SECRET"

GET /v1/calls returns only the 50 most recent calls and cannot reach older records. To keep full call history, subscribe to the call.completed webhook and store each call in your own backend as it arrives.

Resource list

Agents

Create and manage AI agents (prompt, voice, behaviour).

Calls

List, fetch, and trigger calls. Outbound + batch.

Phone numbers

Import numbers from Twilio or Telnyx and attach them to agents.

SMS

Send individual messages and bulk campaigns.

Account

Manage API keys and view usage.

OpenAPI specification

The whole API is described in a machine-readable OpenAPI 3.1 document:

Full URL: https://docs.nixflex.com/api-reference/openapi.json Use it to:

Import every endpoint into Postman or Insomnia - one paste and each request is ready to send, fields included.
Generate a client in your language - run any OpenAPI generator against it for Python, Go, PHP, Ruby, Java, or C#. For Node.js, use the official SDK instead.
Give an AI coding assistant the real shape of the API - tools that read a spec write correct calls instead of guessing field names.

The spec covers authentication, every request and response schema, and the shared error envelope. A few objects with long field lists stay open in the spec and link to the page that documents them in full.

Status codes

Code	Meaning
`200`	Success (GET, PUT, PATCH, DELETE)
`201`	Created (POST)
`400`	Invalid request — check parameters
`401`	Not authenticated — check API key
`403`	Authenticated but not permitted
`404`	Resource not found
`409`	Conflict (e.g. number already imported)
`429`	Rate limited — see `Retry-After` header
`500`	Server error — contact support
`502`	Upstream provider error (Twilio, etc.)

Idempotency

Mutation endpoints (POST, PUT, PATCH, DELETE) accept an optional Idempotency-Key header for safe retries:

Idempotency-Key: my-unique-request-id-123

Requests with the same key within 24 hours return the original response. Safe to retry on network failures.

API

Platform API

API reference

Base URL

Versioning

Authentication

Request format

Response format

Result limits

Resource list

Agents

Calls

Phone numbers

SMS

Account

OpenAPI specification

Status codes

Idempotency

​Base URL

​Versioning

​Authentication

​Request format

​Response format

​Result limits

​Resource list

Agents

Calls

Phone numbers

SMS

Account

​OpenAPI specification

​Status codes

​Idempotency

Base URL

Versioning

Authentication

Request format

Response format

Result limits

Resource list

OpenAPI specification

Status codes

Idempotency