Query String on English home page in multilingual websites

I have problem with google ads it's add query string on the URL with query string and due to that the website return 404 error.

Example :

when you click the below link
https://boutique.celinedion.com/en?test=test
it will redirect to with 404 error.
https://boutique.celinedion.com/en/en?test=test

but in other sites it's work fine example:
https://collection.volvocars.com/en?test=Test
redirect to (but remove the query string but i want to keep it!)
https://collection.volvocars.com/en/

I try to use IIS rewrite rule but it doesn't work

any ideas to fix this problem

Thanks in advance

Put a slash at the end of your original url.
https://boutique.celinedion.com/en/?test=test

Thanks for your reply

yes that what we did as work around, but I need a permanent fix for this issue.

the marking team how are responsible to add the final URL to the google ads so I need to make sure if they didn't add the slash the end of URL, the page will load correctly to not waste our clients ads spend on 404 page.