## ADDED Requirements

### Requirement: Backend URL is configured via environment variable
The frontend application SHALL use the URL defined in the `REACT_APP_BACKEND_URL` environment variable to make API calls to the backend.

#### Scenario: Environment variable is set
- **WHEN** the `REACT_APP_BACKEND_URL` environment variable is set to "http://api.example.com"
- **THEN** the application SHALL make API calls to "http://api.example.com".

#### Scenario: Environment variable is not set
- **WHEN** the `REACT_APP_BACKEND_URL` environment variable is not set
- **THEN** the application SHALL make API calls to "http://localhost:3001".