Hi,
Could you please re-download HikaShop 2.3.0 ?
We made an "hot fix" Friday afternoon for this warning.
Please note that it is not a good thing to display the PHP notice/warnings in a production website, even if we do our best to not have any warning in the code, depending your Joomla version and the plugins you have, you could have "logical" PHP warnings.
It is never a good thing that your users could have information about your website (file path, etc).
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.