Add BuddyPress register link to login modal for AppPresser

register-link.php

<?php
// Author: Scott Bolinger https://apppresser.com
/* Add register link to login modal */

add_action( 'appp_login_modal_after', 'app_register_link' );

function app_register_link() {
	
	if( is_user_logged_in() )
		return;

	echo '<a href="' . home_url() . '/' . BP_REGISTER_SLUG . '" class="register-link">Register</a>';
}