Hello,
Paypal notification is generally dynamic via a parameter that the plugin can provide to Paypal when the customer is redirected to the platform.
But if you have configured a notification url in your paypal account, that URL will be called automatically ; and you need to be sure that this URL is right in HTTPS and not in HTTP.
About worldpay, the plugin is no more in the HikaShop package and because it has been developed by BrainForge, we do not have any knowledge on the code and do not have any test account. So it will be difficult for us to give you more details but you might have a similar problem.
Maybe you can see to tweak you server in order to autorise the HikaShop notification in HTTP ; thus you will be sure that it will continue to work and it will not generate side effects with your customers.
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.