URL’s shown as parameters instead of link prefix

I’ve created a affiliate link and named it ‘Japanse vertaalgids’.
In settings I changed the link prefix to ‘goto’ and I opted not to include the category in the URL. I’m using the default 302 redirects.

My domain is https://www.wapititravel.com/blog/wapiti-staging/
(a staging site)

This is the URL that is generated : https://www.wapititravel.com/blog/wapiti-staging/?thirstylink=japanse-vertaalgids

But I had expected that this would be the result : https://www.wapititravel.com/blog/wapiti-staging/goto/japanse-vertaalgids/

What could be causing this and how to fix this?

The page I need help with: [log in to see the link]