Add to wp-config.php file:
define('FORCE_SSL_ADMIN', true);
if (strpos($_SERVER['HTTP_X_FORWARDED_PROTO'], 'https') !== false){
$_SERVER['HTTPS'] = 'on';
$_SERVER['SERVER_PORT'] = 443;
}
if (isset($_SERVER['HTTP_X_FORWARDED_HOST'])) {
$_SERVER['HTTP_HOST'] = $_SERVER['HTTP_X_FORWARDED_HOST'];
}
define('WP_HOME','https://example.com/');
define('WP_SITEURL','https://example.com/');
Thanks to https://www.aiprose.com/blog/148