URGENT error 0 : Call to undefined method hikashopCartClass::loadCart()

-- url of the page with the problem -- : www.trichi.it/idee-regalo-natale-2019
-- HikaShop version -- : 4.2.2
-- Joomla version -- : 3.9.12

I entered a coupon then I tried to shop to try if everything work but now I get this ugly error!! please please help me I don't know where to fix it, I really didn't touched anything else...

UPDATE:
I trashed my coupon and now seems to work. But obviously I need to create discounts and coupon.
What should I fix?

the errors I get are
<br />
<b>Deprecated</b>: Methods with the same name as their class will not be constructors in a future version of PHP; plgSystemSlideshowckhikashop has a deprecated constructor in <b>/web/htdocs/www.trichi.it/home/plugins/system/slideshowckhikashop/slideshowckhikashop.php</b> on line <b>11</b><br />
<br />
<b>Deprecated</b>: Methods with the same name as their class will not be constructors in a future version of PHP; plgSystemSlideshowckparams has a deprecated constructor in <b>/web/htdocs/www.trichi.it/home/plugins/system/slideshowckparams/slideshowckparams.php</b> on line <b>12</b><br />
<br />
<b>Notice</b>: Constant K2_JVERSION already defined in <b>/web/htdocs/www.trichi.it/home/plugins/system/k2/k2.php</b> on line <b>21</b><br />
<br />
<b>Deprecated</b>: The each() function is deprecated. This message will be suppressed on further calls in <b>/web/htdocs/www.trichi.it/home/plugins/system/falangdriver/falang_database.php</b> on line <b>146</b><br />

Dear,
I have the same issue, here is my logs :
0 Call to undefined method hikashopCheckoutHelper::haveEmptyContent()
Call stack
# Function Location
1 () JROOT/components/com_hikashop/controllers/checkout.php:491
2 checkoutController->checkWorkflowEmptyStep() JROOT/components/com_hikashop/controllers/checkout.php:204
3 checkoutController->show() JROOT/components/com_hikashop/controllers/checkout.php:81
4 checkoutController->step() JROOT/libraries/src/MVC/Controller/BaseController.php:710
5 Joomla\CMS\MVC\Controller\BaseController->execute() JROOT/administrator/components/com_hikashop/helpers/helper.php:2196
6 hikashopController->execute() JROOT/components/com_hikashop/hikashop.php:92
7 require_once() JROOT/libraries/src/Component/ComponentHelper.php:402
8 Joomla\CMS\Component\ComponentHelper::executeComponent() JROOT/libraries/src/Component/ComponentHelper.php:377
9 Joomla\CMS\Component\ComponentHelper::renderComponent() JROOT/libraries/src/Application/SiteApplication.php:194
10 Joomla\CMS\Application\SiteApplication->dispatch() JROOT/libraries/src/Application/SiteApplication.php:233
11 Joomla\CMS\Application\SiteApplication->doExecute() JROOT/libraries/src/Application/CMSApplication.php:196
12 Joomla\CMS\Application\CMSApplication->execute() JROOT/index.php:49

My bad, I had to configure checkout workflow. It is solved.