Firebase Hosting pass variables in url

Question

I'm building an app in Flutter mainly based on IOS and Android. We have a review system, and for new signups we want to collect referalls from past customers.

We will accomplsih it like this:

1. Send API POST email to the referrers,
2. Attached to the email is a URL to our website, we want an ID attached to it.

The thing I want to fix is with the URL. For us to be able to know who the person being reviewed is on the web, I would like to pass the URL like this:

https://example.com/{id}

I am unsure how to do this via Firebase Hosting, which is where we host the site. How can we accomplish passing the ID in the URL?

My Hosting Config looks like this:

"hosting": {
    "public": "build/web",
    "source": "**",
    "ignore": [
      "firebase.json",
      "**/.*",
      "**/node_modules/**"
    ]
  }

Would be really thankful for an explanation! Thanks