Hello,
First we were unable to process ourselves test, because we were unable to register, so can you provide us with the following information so that we can possibly carry out tests.
But I say possibly because I wonder if your solution is not Paypal server side.
In details, it would seem, if we are not mistaken, that this form actually comes from the PayPal server.
This form is the product of the Paypal code, and your configuration in the HikaShop plugin but also in your PayPal Merchant account.
Contact the Paypal Support in order to have more clue about the situation.
Regards