Hello,
1. I can see booking confirmation page on your website.
2. For invoice issue, I can not understand what the issue is.
3. I can not see register link on your website. Please enable membership option on Settings -> General menu.
http://prntscr.com/1d47mqf
Best regards,
Hello,
Please edit /wp-content/themes/citytours/404.php file to edit 404 page.
And please edit /wp-content/themes/citytours/templates/template-login.php file to edit login/register page.
Best regards,