Asking the couple something
Parking, dress code, or anything the site does not say.
If the couple's site has a Questions section, there is a box at the bottom of it. What you write goes to their wedding inbox and they are emailed to say it has arrived — so it does not sit unread in a portal nobody has opened.
Their answer comes back to you by email, so leave an address if you would like one. You do not need your invitation link to ask; anybody reading the site can.