HTTP redirect to a different port

We have multiple websites running on 2 webservers with 6 total ports:

443

8443

9443

10443

11443

12443

What I need to do is redirect the user to one of these URLs and specify the port as well. For example:

If a user goes to https://admin.101com.com, they need to be redirected to https://admin.101com.com:8443

I've written this irule, but I'm getting an error that says "/config/bigip.conf: "Rule ssl8443, HTTP load balancing rules are not available." in line 24"

rule ssl8443 {
if (http_uri matches_regex "https://admin.101com.com") {
    redirect to "https://admin.101com.com:8443" 
  }
  else {
    discard
  }
}

We are load balancing between 2 web servers, one is hosting http://admin1.101com.com and the other, http://admin2.101com.com. Why am I getting this strange load balancing error?

Thanks for any help,