Replace SID to SERVICE_NAME in Oracle connnection string

I'm getting closer in that the payload is succesfully updated and the correct pool is chosen and when I run a tcpdump on the pool member from "other_pool" I can see the updated payload is being received and it replies but for some reason I'm getting a connection closed error from the client (sqlplus) when testing. I can also see from a tcpdump on the client that replies are coming in correctly so it's not a route/SNAT issue.

ERROR: ORA-12537: TNS:connection closed

when CLIENT_ACCEPTED {
    log local0. "in client_accepted event"
    TCP::collect
}
when CLIENT_DATA {
    log local0. "in client_data event"
    set sid_match 0
    log local0. "orig payload length = [TCP::payload length]"
    if { [TCP::payload] contains "CONNECT_DATA=" } {
        log local0. "original payload = [TCP::payload]"
        set service_name "SERVICE_NAME=MY_SERVICE_NAME"
        if { [regsub -all -nocase "SID=MYSID" [TCP::payload] "$service_name" newdata] } {
            log local0. "found a SID match in tcp payload - replacing with $service_name"
            TCP::payload replace 0 [TCP::payload length] ""
            TCP::payload replace 0 0 $newdata
            log local0. "replaced payload = $newdata"
   set sid_match 1
        }
        log local0. "new payload length = [TCP::payload length]"
        if { $sid_match != 0 } {
             log local0. "sending to pool other_pool"
             LB::detach
    pool other_pool
             TCP::release 
        } else {
    do nothing further - found no SID match - use the VS default_pool
    log local0. "No SID match - use the VS default_pool"
             TCP::release 
        }
    }

    TCP::release
    TCP::collect
}

when LB_SELECTED {
    log local0. "selected pool member [LB::server addr]"
}