I can't access wp url parameter - wordpress

Question

I'm trying to add an url parameter to a custom wp rest api endpoint, but when I access the endpoint using this url: mysite.com/wp-json/booking/pris?name=carl, I get this error:
SyntaxError: JSON.parse: unexpected character at line 1 column 1 of the JSON data
Here is my code:
add_action( 'rest_api_init', 'my_register_route_for_price' );
function my_register_route_for_price() {
global $wp;
$wp->add_query_var( 'name' );
register_rest_route( 'booking', 'pris', array(
'methods' => 'GET',
'callback' => 'get_price_callback',
)
);
}
function get_price_callback() {
$param = $request->get_url_params( 'name' );
return rest_ensure_response($param);
}

Answer 1

That's a WordPress security feature.
Undefined WordPress query variable outside the scope of the WP_Query class need to be defined first.
WP::add_query_var( string $qv )
Adds a query variable to the list of public query variables.
Use Case Scenario
<?php
add_action( 'init','wp67408336' );
function wp67408336() {
global $wp;
$wp->add_query_var( 'name' );
};
In any case
<?php
$name = htmlspecialchars( $_GET["name"] );