Https not working for ipad and iphone

I have some problems with ipad when customer go to checkout

https://www.asilla.dk/onepagecheckout

on the last step in the chekout customer click on confirm and my
payment pages opens and same time the url changes to

http://www.asilla.dk/Plugins/PaymentePay/Open

https  changes to http and ipad comes with a warnig the the form is not secure.

The oayment window is secure and i dont have this problem on other browsers.

How can i change  http://www.asilla.dk/Plugins/PaymentePay/Open

to https://www.asilla.dk/Plugins/PaymentePay/Open

This seems to be related to the payment plugin itself. That means the payment plugin is not enforcing HTTPS correctly. Perhaps you can contact the developer directly. :)