Cannot exclude particular post from loop of custom post type

I have a custom post type (from a theme installed by previous developer), and here is the code of loop which retrive the post and display them.

<?php
// Counter
$post_count = 1;

// Query
$gp_query_args = array(
    'post_type'         => 'event',

    //EXCLUDE Events try by me
    'post__not_in' => array('1646'),
    // exclude event try code block ends

    'meta_key'          => 'gp_event_date',
    'meta_value'        => date('Y/m/d'),
    'meta_compare'      => '>=',
    'orderby'           => 'meta_value',
    'order'             => 'ASC',
    'posts_per_page'    => -1

);
$gp_query = NULL;
$gp_query = new WP_Query($gp_query_args);

I want to exclude certain events (post of custom post type, from loop), and as you can see i tried using ‘post__not_in’ => array(‘1646’), where 1646 is the post id i see when i edit the custom post . So i guess this is universal post id, not custom post type specific id. But No Matter, the post is not being excluded 🙁

Am i doing wrong??

Edit1:

I found a repository on github ( https://github.com/tiffanytse/breadbyus-wordpress/blob/master/linguini/template-event.php ) that is exactly similar to my theme structure. I dont know the theme name, so i’m not sure whether that’s the same theme on the site i’m working over.