wp_set_object_terms "invalid taxonomy" in own Class

Hello, faced with such a problem.
I have Custom post type with Taxonomy, in the functions.php file writing script

function addCategory($post){
        $terms = $post['terms'];
        $post_id = $post['id'];
        $taxonomy = 'my_taxonomy_name';
$term_taxonomy_ids = wp_set_object_terms( $id, $terms, $taxonomy, true);
}
addCategory($post);

everything works, the category is added to the post

But when I try to do the same in the class I get an error “invalid taxonomy”

class MyClass{
    function addCategory( $post ){
        $terms = $post['terms'];
        $id = $post['id'];
        $taxonomy = 'my_taxonomy_name';
$term_taxonomy_ids = wp_set_object_terms( $id, $terms, $taxonomy, true );
        if ( is_wp_error( $term_taxonomy_ids ) ) {
            echo $term_taxonomy_ids->get_error_message(); // "invalid taxonomy"
        }
    }
}
$MyClass= new MyClass;
$MyClass -> addCategory($_POST); // "invalid taxonomy"