iRule is not working, HTTP::payload ?

Am trying to check http traffic if it has a specified string, and pass it, or block it if not.

but this traffic is confined to one network.

this is the iRule:

when HTTP_REQUEST

{

 if { [IP::addr [IP::client_addr] equals 10.0.0.0/24] }

{

 HTTP::collect 20

   set HTTP::payload [string tolower HTTP::payload]

      if { not ( [HTTP::payload] contains "ivrTransactionID" )}

        { reject }

        HTTP::release

}

}