add custom id in URL

Hello there,

I’m running a cashback site and I need to keep track of the user who click s on my affiliate link.
Therefore I have to add a specific parameter at the end of the URL.

Instead of having : https://www.merchant.com/?ref=mysite
I have something like that : https://www.merchant.com/?ref=mysite?userid=415

The userid is (obviously) added dynamically and I can’t see (yet) how thirstyAffiliate can manage that.

My basic configuration is :
link name : merchant
destination URL : https://www.merchant.com/?ref=mysite
=> cloaked url : https://www.mysite.com/go/merchant/

I thought that using the following link : https://www.mysite.com/go/merchant/?userid=415 would do the trick, but it does not.

Thanks for your help !

https://www.ads-software.com/plugins/thirstyaffiliates/