Hi,
As you can see in the OKPay plugin details (or xml), the plugin has not been developed by the HikaShop team but by "DigitalArtJoomla" in 2012.
After that, regarding the plugin code, that's right that it just send the products and not the order total ; which is something we never do for our plugins.
Because we do not have any documentation or test account ; because that's not a plugin we developed, I will remove the OKPay plugin from the HikaShop packages and that plugin will be released in github, like other plugin that external developers shared with the HikaShop team (under open source license).
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.