Hello,
HikaShop 3 comes with a "cart notify" plugin to display a tooltip or a popup when a product is added into the cart.
www.hikashop.com/home/blog/367-hikashop-3-0-out.html#cart
If that plugin is unpublish, the customer will be redirected to the checkout page.
But in your case, you're using the legacy mode, so the redirection is made via these settings :
www.hikashop.com/support/documentation/5...html#advanced_legacy
And you have a fatal error in your checkout.
That's why the checkout page is not complete and that you do not see your template.
You should take a look at your PHP error log in order to get the fatal error details (full message, file and line of the error).
Only with the details of the error we will be able to give you a procedure to correct the issue.
Regards,
Jerome - Obsidev.com
HikaMarket & HikaSerial developer / HikaShop core dev team.
Also helping the HikaShop support team when having some time or couldn't sleep.
By the way, do not send me private message, use the "contact us" form instead.