Getting moved to productdetails

[velomobilcenter]

When ever i choose a tiresize in my options i get booted to the productdestription instead of just beeing able to add the size to my cart.

I tried to put in the "ontop" in layout position in the Multi variant custom field though it doesnt work, anyone got an idea what im doing wrong?

url : https://www.velomobilcenter.dk/index.php/admin-testsider/webshop/dæk

VM : 3.09