Unable to edit any payment option

-- HikaShop version -- : 3.2.1
-- Joomla version -- : 3.8.2
-- PHP version -- : 5.6.32
-- Browser(s) name and version -- : Version 57.0.1 (64-bit)

Hi there,

When I click on one of the payment methods to edit it, eg. HikaShop bank transfer payment plugin

Then it takes me to a page where the CSS doesn't load and the page does not show properly, the URL on my side is:

https://www.**********.co.za/administrator/index.php?option=com_hikashop&ctrl=plugins&task=edit&name=banktransfer&plugin_type=payment&subtask=edit

Please could you help me fix this.

Thanks,
Charles