Source NAT based on XFF header

I'm trying to configure this irule

when HTTP_REQUEST {

    if { [class match [HTTP::header values "X-Forwarded-For"] equals XFF_SourceNAT] } {
    log local0.alert "Matched XFF [HTTP::header values "X-Forwarded-For"] to group"
        set category [class match -value [HTTP::header values "X-Forwarded-For"] equals XFF_SourceNAT]
       log local0.alert "Setting category to $category"

 NAT traffic according to xforwarded-for header
            snatpool $category
    } else {
    log local0. "No X-Forwarded-For header found."
     either for websense updates or traffic is not hitting the xff datagroup
            if { [[IP::client_addr] equals 192.168.182.0/16] } 
    {
    pool FW-Pool
    } else {
    drop

    }
}
}

And in datagroup XFF_SourceNAT {address type) I configured:

172.28.0.0/16:= 2.2.2.2

But in the /var/log/ltm is see the follwoing error:

`Jan 23 21:22:49 slot2/f5 err tmm5[9013]: 01220001:3: TCL error: /partition1/SNAT-XFF-irule  - bad IP network address format (line 1)invalid IP match item  for IP class /ORT/XFF_SourceNAT (line 1)     invoked from within "class match [HTTP::header values "X-Forwarded-For"] equals XFF_SourceNAT"


What can be done to fix the issue?