Error: "Could not instantiate mail function"

Hello

I have attached a screenshot from the checkout on my site. I get the error when I tried typing in my old username and also when I tried to register a new account.

Any idea what may be going on here?

Hi,

HikaShop use the Joomla Mail system to send emails.
Your website is configure to use "php mail function" to send email but this function could be forbidden on some web hosting.
Please configure the Joomla options in order to use another mail system (smtp, sendmail) and check with you web hosting.

This option is a Joomla option in : (menu) Site > (menu item) Global Configuration > (tab) Server > (zone) Mail Settings > (option) Mailer

Regards,