Hi,
The 405 message came after 3.1min of wait ; for me it's more a timeout than a real 405.
Or your error page ressources are not allowed by your nginx and you got a 405 instead of an error page.
Please check your checkout workflow configuration, your PHP error log and the published 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.