How to register an endpoint in the WordPress REST API #wcfra

register-rest-route.php

<?php
	add_action( 'rest_api_init', 'my_own_restroute' );
	function my_own_restroute() {
		register_rest_route(
			'my-namespace/v1',
			'/route/',
			array(
				'methods'  => 'GET',
				'callback' => 'my_restroute_callback',
				'args'     => array(
					'id'   => array(
						'validate_callback' => function($param, $request, $key) {
							return is_numeric( $param );
						},
						'sanitize_callback' => function($param, $request, $key) {
							return (int) $param;
						},
						'required'          => true,
						//'default'           => 1,
						'description'       => 'The ID of the object.',
					),
				),
			)
		);
	}

	function my_restroute_callback( $request ) {
		$data['id'] = $request['id'];
		return $data;
	}
?>