# Error 200: Partner Key Not Found

PayMe's message with `language: "en"`: **Merchant was not found**

The `payme_client_key` or `PayMe-Partner-Key` matches no partner. HTTP 500, with `status_additional_info` `payme_client_key`.

## Usual causes

- A seller sent its own MPL in `payme_client_key`.
- A production key sent to the sandbox, or the reverse.

## What to do

- A direct seller removes the field and sends `seller_payme_id` alone.
- A partner checks the key and the environment. See [Authentication](/payments/getting-started/authentication).

The full list of codes is on [Errors](/payments/getting-started/errors). If something else is going on, see [Troubleshooting by Symptom](/agents/errors/troubleshooting).