## Add

`express.users.add(strexpress_customer_id, UserAddParams**kwargs)  -> UserAddResponse`

**post** `/v1/express/{expressCustomerId}/users`

Associates an existing user with a customer, granting them access to customer-specific resources and studies.

### Parameters

- `express_customer_id: str`

  Unique Express customer identifier. Format: cus_{32-hex-chars}

- `user_id: str`

  User ID to add to the Express customer. Format: usr_{32-hex-chars}

### Returns

- `class UserAddResponse: …`

  Standard success response with optional message

  - `success: bool`

  - `message: Optional[str]`

### Example

```python
import os
from avara import Avara

client = Avara(
    api_key=os.environ.get("AVARA_API_KEY"),  # This is the default and can be omitted
)
response = client.express.users.add(
    express_customer_id="cus_1234567890abcdef1234567890abcdef",
    user_id="usr_1234567890abcdef1234567890abcdef",
)
print(response.success)
```