Custom route endpoint for WP-REST API gives "code": "rest_no_route", error
<p>I am following <a href="https://deliciousbrains.com/wp-rest-api-customizing-endpoints-adding-new-ones/" rel="noreferrer">this</a> tutorial to create custom end points to WP-API .</p>

<p>I am always getting this error  on hitting <strong>/wp-json/custom-plugin/v2/get-all-post-ids/</strong> on <strong>postman</strong> to test : </p>

<pre><code>{
    "code": "rest_no_route",
    "message": "No route was found matching
    the URL and request method ", 
    "data": {
        "status": 404
    }
}
</code></pre>

<p>I have created a custom-plugin.php file in /plugins/custom-plugin/ directory .</p>

<pre><code>&lt;?php
    if ( ! defined( 'ABSPATH' ) ) exit;

    add_action( 'rest_api_init', 'dt_register_api_hooks' );

    function dt_register_api_hooks() {    

        register_rest_route( 'custom-plugin/v2', '/get-all-post-ids/', array(
            'methods' =&gt; 'GET',
            'callback' =&gt; 'dt_get_all_post_ids',
            ) 
            );
    }
    // Return all post IDs
    function dt_get_all_post_ids() {
        if ( false === ( $all_post_ids = get_transient( 'dt_all_post_ids' ) ) ) {
            $all_post_ids = get_posts( array(
                'numberposts' =&gt; -1,
                'post_type'   =&gt; 'post',
                'fields'      =&gt; 'ids',
            ) );
            // cache for 2 hours
            set_transient( 'dt_all_post_ids', $all_post_ids, 60*60*2 );
        }
        return $all_post_ids;
    }
?&gt;
</code></pre>