irule for x forwarder

Dear Yann/Kasi , I had modified the irule , which means i will disable X forwarder for kib.apps.abc.com . And rest other FQDN will have X forwarder enabled . After implementing this irule . Kib.apps.abc.com is working fine , for rest other FQDN i am getting 503 error . Kindly advise me on this

when HTTP_REQUEST { if { !([HTTP::host] eq "kib.apps.abc.com") } { HTTP::header insert "X-Forwarded-For" [getfield [IP::client_addr] "%" 1] } }