# TLS alert: unknown_ca

Independent and unofficial. Not affiliated with or endorsed by any broker or platform named here. Educational only: nothing here is advice, and nothing here recommends a broker or a trade.

This is the markdown version of https://openbrokerapi.com/errors/tls/unknown-ca, written from the same records as that page.

Risk warning: CFDs and spread bets are complex instruments and come with a high risk of losing money rapidly due to leverage. You can lose money on these products, and each provider publishes its own loss figure under FCA rules. You should consider whether you understand how they work and whether you can afford to take the high risk of losing your money. Automated and API trading can amplify losses through bugs, connectivity failures and runaway orders.

As text you can copy:

```
unknown_ca
```

- Kind: Alert
- Where you meet it: While a secure connection is being set up or used
- Read from: [RFC 8446, The Transport Layer Security (TLS) Protocol Version 1.3, section 6.2](https://www.rfc-editor.org/rfc/rfc8446.html#section-6.2)
- Status: verified. Source: [rfc-editor.org](https://www.rfc-editor.org/rfc/rfc8446.html#section-6.2), checked 2026-10-09.

## What does unknown_ca mean in TLS?

A valid certificate chain or partial chain was received, but the certificate was not accepted because the CA certificate could not be located or could not be matched with a known trust anchor.

## What it means in trading API work

The certificate chain leads to an authority your system does not trust. Usual causes are an out of date store of root certificates, a corporate proxy that signs traffic again with its own certificate, or a server that sends an incomplete chain.

This part is this site's own explanation, written for people learning to call a trading API. It is not part of the source cited above and it describes no particular broker.

## What should I do about unknown_ca?

Update the root certificates of the operating system or the runtime. On a corporate network, ask how its proxy certificate is meant to be trusted. Do not disable verification.

This page is an independent explanation in plain words. The definition itself is in [the source it was read from](https://www.rfc-editor.org/rfc/rfc8446.html#section-6.2), which is the authority if the two ever differ.

## Where to go next

- [Everything decoded for TLS](https://openbrokerapi.com/errors/tls)
- [Getting started with API trading](https://openbrokerapi.com/guides/getting-started-with-api-trading): What an API is, what you need and how to make a first call safely.
- [Brokers](https://openbrokerapi.com/brokers): The record for each broker: access, limits, endpoints and error codes.
- [Platform APIs](https://openbrokerapi.com/platforms): APIs that belong to trading software offered by many brokers.
- [Error codes](https://openbrokerapi.com/errors): What each error means, and the fix where the source gives one.

## Licence and how to cite

The records behind this page are all rights reserved. This file is the page itself, at its own address, in another format. It is not part of the CC BY 4.0 downloads listed at https://openbrokerapi.com/data. Quote from it with a link to the page.

Cite as: TLS alert: unknown_ca. Broker API Hub, https://openbrokerapi.com/errors/tls/unknown-ca, newest check 2026-10-09.

Where you rely on a single figure, cite the source and the checked date printed beside it as well. Where this page and a broker's own documentation differ, the documentation wins.