El parámetro de cadena no se puede enviar al archivo de patrón de WordPress

Este código funciona bien:

   function register_custom_patterns() {
        $vari = 5;
        register_block_pattern(
            'twentytwentyfive/asif', // The pattern slug
            array(
                'title'       => __( 'Test Pattern', 'twentytwentyfive' ),
                'description' => __( 'A custom test pattern for the theme.', 'twentytwentyfive' ),
                'content'     => file_get_contents( get_template_directory_uri() . '/patterns/asif.php?id='. $vari), // Path to your custom PHP file
            )
        );
    }
    add_action( 'init', 'register_custom_patterns' );

Pero no funciona:

function register_custom_patterns() {
    $vari = "Send me";
    register_block_pattern(
        'twentytwentyfive/asif', // The pattern slug
        array(
            'title'       => __( 'Test Pattern', 'twentytwentyfive' ),
            'description' => __( 'A custom test pattern for the theme.', 'twentytwentyfive' ),
            'content'     => file_get_contents( get_template_directory_uri() . '/patterns/asif.php?id='. $vari), // Path to your custom PHP file
        )
    );
}
add_action( 'init', 'register_custom_patterns' );

Error:

http://localhost/asif_wp/wp-content/themes/twentytwentyfive/patterns/asif.php?id=Send me): failed to open stream: HTTP request failed! HTTP/1.1 400 Bad Request in C:\xampp\htdocs\asif_wp\wp-content\themes\twentytwentyfive\functions.php on line 168

En breve:

Parámetro

        $vari = 5;  // Working
        $vari = "Show me";  //Error

¿Por qué y cómo solucionarlo?