Hikashop + PHP 7.3 not compatible?

-- HikaShop version -- : 4.2.3
-- Joomla version -- : 3.9.16
-- PHP version -- : 7.3
-- Browser(s) name and version -- : Chrome 80.0.3987.149
-- Error-message(debug-mod must be tuned on) -- : Error: 0

Hi,

my Hikashop 4.2.3 works fine with PHP 7.2.
But when I switch to PHP 7.3 or even 7.4 is stops working - after clicking "Proceed to checkout" I get the error you can see in the attachment.

So is Hikashop not compatible with PHP 7.3 or what exactly should I do to make it work with higher version than 7.2.

Thanks.