Hello,
Sorry if my previous message was not clear enough ; a "custom plugin" means that it requires a custom development.
The documentation link I gave you is the developer documentation, to help people (with some development/PHP knowledge) with the HikaMarket triggers for their developments of plugins.
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.