I can pass integer values to WP REST API. But, cannot pass non-numeric characters. It gives error. 

This is what I used...

```
add_action( 'rest_api_init', function () {
    register_rest_route( 'crowdapi/v1', '/register/(?P<id>\d+)/(?P<username>\d+)', array(
        'methods' => 'POST',
        'callback' => 'userCheck',
    ) );
} );

```

Any idea how to pass strings as well.. ?