CODE EXAMPLE FOR PHP

woocommerce check if user is logged in

add_action( 'template_redirect', 'check_if_loggedin' );
function check_if_loggedin() 
{
	if(!is_user_logged_in())
	{
			echo '
					<script>
						alert("You must be logged in to access this page.
You will be redirected to the login page.");
						window.location.href = "https://example.com/login";
					</script>
				';
	}
}