Hi,
This URL is the URL of the page the customer sees after clicking on the "register" button. It displays a message explaining to the customer that they need to click on the URL sent to them by email.
The activation URL in the email is also a HikaShop URL. When you click on that link, the browser of the user will open a page with the URL index.php?option=com_hikashop&ctrl=user&task=activate&activation=1...
On this page, HikaShop will first make sure that the registration and activation are possible based on the settings of the Joomla user manager. Then, it will call the Joomla user model to activate the user, with code like this:
$model = $this->getModel('Registration', 'UsersModel',array(),true);
$language = JFactory::getLanguage();
$language->load('com_users', JPATH_SITE, $language->getTag(), true);
if($model)
$result = $model->activate($activation);
If the activation is successful, it will display a success message and potentially redirect somewhere else (for example, if you registered from the checkout of HikaShop, it will redirect you back to the checkout so that you can proceed to your purchase).
If the activation fails for some reason, it will display an error message, which should explain what the problem is.
You're saying that the activation fails. What error message did you get then ?