can’t get url parameters working with metadata for searching posts

I am trying to get a custom feild added as a search paramter url.

my post metadata for this example is ‘public_paywall’ and want to register as it as a query var “access”

This is the code I have tried to no avail:

/////////////register var//////////////

function myplugin_register_query_vars( $vars ) {
    $vars[] = 'access';
    return $vars;
}
add_filter( 'query_vars', 'myplugin_register_query_vars' );

////////////add ///////////////////

function myplugin_pre_get_posts( $query ) {
    // check if the user is requesting an admin page 
    // or current query is not the main query
    if ( is_admin() || ! $query->is_main_query() ){
        return;
    }

    // edit the query only when post type is 'food'
    // if it isn't, return
    if ( !is_post_type_archive( 'post' ) ){
        return;
    }

    $meta_query = array();

    // add meta_query elements
    if( !empty( get_query_var( 'access' ) ) ){
        $meta_query[] = array( 'key' => 'public_paywall', 'value' => get_query_var( 'access' ), 'compare' => 'LIKE' );
    }

    if( count( $meta_query ) > 1 ){
        $meta_query['relation'] = 'AND';
    }

    if( count( $meta_query ) > 0 ){
        $query->set( 'meta_query', $meta_query );
    }
}
add_action( 'pre_get_posts', 'myplugin_pre_get_posts', 1 ); 

I have posts with the value ‘paywall’ for the key ‘public_paywall’but my search urls dont work:

http://localhost/vraudiogigscom/?post_type=post&access=paywall

what am I doing wrong? I have been searching other examples and not getting anywhere

cheers