This is coming in very late but i am sure you already have this resolved. I am leaving this just incase someone else has this issue. There are some things to check when this happens. i.e(The cookies not getting set properly in the browse)

1. check if the tracking scripts are added correctly on y our production website.
2. check if the referral id you added to the link exists as a promoter.
3. FirstPromoter sets its cookies on the primary domain so if you are using a sub domain of vercel,ngrok, azure etc that would not work as expected.