# Get User Identifiers

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Client SDK
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Backend API
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Mobile approve
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SSO
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Sub-journey
> Retrieves all known user identifier from the user's profile in Transmit


## Description

This journey step is used to obtain all the known identifiers for a user. You would typically use this step after getting a user identifier from the user, e.g. via [Collect information](/guides/orchestration/journeys/get_info_from_client) journey step. This allows you to invoke other steps or APIs that might require a different identifier. An example would be a flow where the users provide their legacy identifier from an external IDP when requested for a user identifier, but a follow up action requires the internal `Platform User ID` (also known as `User ID`). You would use this step to translate to the correct identifier.

## Configuration

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| Field | Description |
|  --- | --- |
| Input User Identifier Type | Choose between `External User ID` for an ID from an external IDP, or `Platform User ID` for the Mosaic user ID. |
| User Identifier | Enter an expression that contains the user identifier, such as a variable from a [Collect information](/guides/orchestration/journeys/get_info_from_client) step. The step will look up the user according to this value, based on the identifier type provided above. |
| Output Variable | This will contain the user identifiers in JSON format if the user is found, with fields `email`, `external_user_id`, `phone`, `platform_user_id` and `username`. |
| Error Output Variable | A variable to store any errors, specifically if the user is not found, for error handling procedures. |


## Example

**Output variable structure**:


```json
{
  "email": "user@example.com", // Email
  "external_user_id": "EXT123456", // External User ID
  "phone": "+1234567890", // Phone
  "platform_user_id": "xovgrhzbnple2y7oebahm", // User ID
  "username": "username123" // Username
}
```

**Error output variable**:


```json
{
  "error": "unknown_user",
  "description": "Could not find user by identifier"
}
```