Hi,
I don't understand your message.
In the dropdown "Force a menu on the checkout", you would see all Joomla menus.
I think it is logical that you can't find the checkout page, because it is menus.
The option "force a menu" is to indicate which menu target your checkout page. So, all links which would redirect the user to the checkout page, would use the checkout menu.
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.