Unable to make changes in backend HikaShop configuration

-- url of the page with the problem -- : Backend management
-- HikaShop version -- : 4.0.3
-- Joomla version -- : 3.9.6
-- PHP version -- : 7.2.16
-- Error-message(debug-mod must be tuned on) -- : "Forbidden
You don't have permission to access /administrator/index.php on this server."

I have a site on a PCI compliant server hosted at CloudAccess.net and I am not able to use changes to my HikaShop settings from the Joomla back-end.

I have tried to change a number of settings. One setting I need to change and have tried to change is to have the tax calculations based on the shipping address instead of the billing address.

The error message I am getting when I try to change that setting and save the changes is: :

"Forbidden
You don't have permission to access /administrator/index.php on this server."

So, I am wondering if you know of a solution to this issue? I had figured this was an issue with the hosting setup at cloudaccess.net but they have looked at it and state they believe it is a HikaShop configuration issue.

Here is their exact response:

"I reset the file ownership/permissions for your website but that didn't fix it. I also checked the ACL settings you have on the site but those seem to be correct as well. I must conclude that the issue is not with Joomla or our server config but with Hikashop, especially since we didn't have reports of this issue in the past. I'm afraid that as we don't support 3rd party extensions, we can't help you with this - you will need to consult Hikashop support on that. If they troubleshoot the problem and point to a specific issue on our end that we might not have thought of since our expertise with 3rd party extensions is limited, we will be more than happy to look into it."