Hi,
The payment log report is field by payment plugin only if the debug mode is activated.
So, if your payment log is empty, it maybe not a real problem.
After that, if your payment plugin is in debug mode and your log is empty, you could check permissions on the file, see if Joomla can write.
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.