Install and update

// wp-config.php

if (isset($_SERVER["HTTP_ORIGIN"]) === true) {
	$origin = $_SERVER["HTTP_ORIGIN"];

        // $allowed_origins is an array of domains to be allowed; it could as well be filled by all active languages urls from WPML
	$allowed_origins = array(
					"https://www.domain1.com",
					"https://www.domain2.com"
	);
	if (in_array($origin, $allowed_origins, true) === true) {
					header('Access-Control-Allow-Origin: ' . $origin);
					header('Access-Control-Allow-Credentials: true');
					header('Access-Control-Allow-Methods: POST');
					header('Access-Control-Allow-Headers: Content-Type');
	}
	if ($_SERVER["REQUEST_METHOD"] === "OPTIONS") {
					exit; // OPTIONS request wants only the policy, we can stop here
	}
}

get_rest_url()

site_url()

$rest_url = site_url() . '/wp-json/';