Please try in a different browser or on a different mobile before contacting support about the page not working. Different computers and mobiles have different browsers which may mean that the page may not work properly on older mobiles and browsers.

You can register up to 3 registration numbers for your parking permit.
See manual here

In 90% of cases, this is because you have not authorized your card to pay online. Log in to your bank and allow the card to be used for online payments.

First of all, you should check your spam folder on your email account and make sure that the email has not ended up there. If you still cannot find any email even though you are sure that you have entered the correct address, then try creating a new account with a different email address.