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

# Alias Endpoint

> POST /api/alias - Merge user identities (optional)

## POST /api/alias

Merges user identities. This endpoint is optional but recommended for preserving event history when users sign up.

## Request

### Headers

<ParamField header="Content-Type" type="string" required>
  `application/json`
</ParamField>

<ParamField header="X-Api-Key" type="string" required>
  Your API key
</ParamField>

### Body

<ParamField body="userId" type="string" required>
  New user ID (the identified user ID)
</ParamField>

<ParamField body="previousId" type="string" required>
  Previous user ID (usually the anonymous ID)
</ParamField>

<ParamField body="timestamp" type="string" required>
  ISO 8601 timestamp
</ParamField>

### Example Request

```bash theme={null}
curl -X POST https://api.solute.dev/api/alias \
  -H "Content-Type: application/json" \
  -H "X-Api-Key: your_api_key" \
  -d '{
    "userId": "user_123",
    "previousId": "anon_456",
    "timestamp": "2025-01-15T10:30:00Z"
  }'
```

## Response

### Success Response

<ParamField body="success" type="boolean" required>
  `true` if the request was successful
</ParamField>

<ParamField body="userId" type="string" required>
  The new user ID
</ParamField>

<ParamField body="previousId" type="string" required>
  The previous user ID
</ParamField>

### Example Response

```json theme={null}
{
  "success": true,
  "userId": "user_123",
  "previousId": "anon_456"
}
```

## Use Case

This endpoint is typically called when a user signs up. It merges their anonymous identity with their new user ID, ensuring all events from before signup are associated with the user.

## Related

<CardGroup cols={2}>
  <Card title="Identify Endpoint" icon="user" href="/backend-api/identify" />

  <Card title="Group Endpoint" icon="users" href="/backend-api/group" />
</CardGroup>