Need help with some code

I am building affiliate software with RoR. Although I am a beginner but I am still good experience with RoR. I am trying to build refferal program, like Rewardful, multi-vendor. I implemented it in my own website with url params (example.com?refferal=...) , I don't know how to implement it with other vendors. Which is , a person will create referral program for his product and will now allow other affiliate promoters (or referers) to create and share their link with others. Later the visitor will get tracked and after he does successful payment the refferer will get commission. (Payment wala part I can implement with stripe metadata) What I need help with is how to track visitors on other website? For eg. Rewardful asks us to put javascript code our website. Do I need javascript code too for my clients to paste it in their website, how do I create it and how does it sends request to my server? Anyone?? P.S, I am using Ruby on rails framework. Will appreciate your help.