---
title: "Invitation already used — Anis Developers"
description: "This invitation has already taken a key — for example, the key submission was sent again after its answer was lost. An invitation takes exactly one key."
url: https://developers.anis.ly/errors/key-duplicate/
language: en
---

> Every page of this documentation: https://developers.anis.ly/llms.txt

[Error codes](https://developers.anis.ly/errors.md) · Enrolling a key

# Invitation already used

- **Code:** `key_duplicate`
- **Status:** 409
- **If this was an order:** Never returned when buying
- **Send it again unchanged?** No — change something first
- **.NET SDK:** `EnrollmentRefusedException`

## What it means

This invitation has already taken a key — for example, the key submission was sent again after its answer was lost. An invitation takes exactly one key.

## What to do

- Ask Anis staff to restart the enrolment; it issues a new invitation. A new key pair on the same invitation is refused the same way.
- Next time, save the key submission’s answer (it carries the challenge) before anything else.

## Where you can meet it

- POST [Submit a public key](https://developers.anis.ly/reference/submit-key.md) `/v1/enrollments/{invitationId}/keys`

## Example

The body of the refusal. Its `type` is the address of this page.

```
{
  "type": "https://developers.anis.ly/errors/key-duplicate",
  "title": "Invitation already used",
  "status": 409,
  "code": "key_duplicate",
  "requestId": "01J9R2K8T4V6XQ0M3B7C5D9E1F"
}
```