> ## Documentation Index
> Fetch the complete documentation index at: https://docs.usefrictionless.com/llms.txt
> Use this file to discover all available pages before exploring further.

# API reference

> The Context API: base URL, authentication, limits and errors.

```text Base URL theme={null}
https://api.usefrictionless.com/api/v1
```

Send JSON, with your API key in the `Authorization` header as `Bearer fk_live_…`. Create the key in **Settings → Developers**; [API keys and secrets](/authentication) explains each secret.

The API only accepts calls from servers. Browsers are blocked so the key can't leak through a web page. The **Try it** button on each endpoint still works, because Mintlify sends the request from its servers.

The Context API is on the **Pro** plan and above.

## Limits

| What | Limit |
| - | - |
| `userId` | 1 to 128 letters, numbers or `_ . : @ + -` |
| Attribute and property keys | Up to 40 letters, numbers, spaces, dots, dashes or underscores |
| Values | Text up to 500 characters, numbers, or true/false. No nested objects. |
| Attributes per contact | 50 per request, 100 in total |
| Properties per event | 20 |
| Event name | 120 characters |
| Phone | 7 to 15 digits with the country code, like `+2348012345678` |
| Requests | 300 a minute per API key |

## Errors

Errors come back as `{ "error": { "code": "...", "message": "..." } }`. The message says what to fix.

| Status | Code | Meaning |
| - | - | - |
| 400 | `invalid_request`, `invalid_user_id` | Something in the request is missing or the wrong shape. |
| 401 | `missing_key`, `invalid_key` | No API key, or one that was rotated. |
| 402 | `plan_required` | Your workspace isn't on a plan with the Context API. Upgrade under Billing. |
| 404 | `contact_not_found`, `customer_not_found` | No contact with that `userId`, or nobody with that phone has chatted yet. |
| 429 | `rate_limited` | Over 300 requests a minute. Wait and retry. |
| 500 | `server_error` | Our side. Retry with a short backoff. |


This documentation is built and hosted on [Mintlify](https://mintlify.com), a developer documentation platform.