Membership Plugin IPN and redirect

Hi,
I've just installed Membership Premium, all works fine except when paying with paypal (redirection and IPN). The form which gets posted to paypal has:
<input type="hidden" name="notify_url" value="/paymentreturn/paypalexpress">
<input type="hidden" name="return" value="/thank-you-register/">

So none of these work, if I change the live html using the inspector (webdev tools) to
<input type="hidden" name="notify_url" value="www.mysite.com/paymentreturn/paypalexpress">
<input type="hidden" name="notify_url" value="www.mysite.com/paymentreturn/paypalexpress">
<input type="hidden" name="return" value="/thank-you-register/">

Redirection and IPN work fine.

Why is http://www.mysite.com not in the fields? Can someone please tell me how to do it?