Irule direct traffic to external site

Traffic arrives at an existing VIP  www.mycompany.com/pay1

When the URI is pay1, I have to send a connection to an external web site 

"*pay1" {
set dest_host [RESOLV::lookup @8.8.8.8 "www.externalsite.com"]
}
HTTP::uri "/merchant.jsp"

}

HTTP::header replace host $dest_host
node $dest_host 443

External site recently changed their process to no longer allow IP address connections, the issue
is that I cannot figure out how to forward the required traffic to the external site via the irule.

I think that this is how the F5 is sending the external traffic, and this gives me an error.

curl --header 'Host: www.externalsite.com' https://192.168.1.1/merchant.jsp

THis works as expected via curl

curl -kv https://www.externalsite.com/merchant.jsp

Any bright ideas how to modify the irule to allow the connection as per the bottom section?

Tried this and it didn't work

HTTP::header replace host www.externalsite.com
node $dest_host 443

do not want to hardcode the IP's in the irule.