On the Affiliate Links > Settings > General page you can find the “Pass Along Query Paramters” setting:
When enabled, any query parameters added to the shortlink will get passed along to the destination URL.
As an example, you could have this shortlink:
https://www.mysite.com/recommends/webshop
That redirects to this destination URL:
https://www.webshop.com?affiliate=456
With the setting enabled, if you now add a query parameter like this:
https://www.mysite.com/recommends/webshop?product=123
It will pass that product=123 parameter along to the destination URL by redirecting to this destination:
https://www.webshop.com?affiliate=456&product=123