Hi,
To implement a payment method, you need to use a plugin. Else it will not work properly.
Without using a plugin, all the HikaShop actions for order creation, emails, product stock... will not be used.
We are not creating this plugin actually, and we have a lot of work. So this will not be made shortly.
I suggest you to post you request in the commercial jobs section of this website, or ask to a third developer, or develop it yourself.
You can find some documentation here:
www.hikashop.com/en/support/documentatio...r-documentation.html
And can see how the others payment plugins are made.