Hello,
I can only help regarding the Stripe V3 issue ; not the Paypal one.
Please open another thread for that issue.
Regarding the logs, you have to open your HikaShop configuration page and click on the button "see the report" as visible/explained in the documentation page I gave you.
That log is there to store the error for payment plugins, its helps the debugging since it contains data that we don't want to let the customer see.
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.