I am adding a new class to my body tag if the logged in user is subscriber, need help

Question

Please try this code instead-

add_filter( 'body_class', 'wpse_268176_body_class' );

function wpse_268176_body_class( $classes ) {

    $user = wp_get_current_user();

    if ( in_array( 'subscriber', $user->roles ) ) {
        $classes[] = 'class-name'; // your custom class name
    }

    return $classes;
}

Place this in your active theme’s functions.php file.

[Thanks Dave Romsey for your suggestion.]