stream profile encoding issue

i got an error when i add STREAM::encoding utf-8 into this iRule 01070151:3: Rule [/Common/korabia3] error: /Common/korabia3:5: error: [command is not valid in current event context (HTTP_RESPONSE)][STREAM::encoding utf-8]

can someone help me with this? where should i put STREAM::encoding utf-8 in this iRule?

when HTTP_RESPONSE {

    STREAM::disable
 if { [HTTP::header Content-Type] contains "text" } {
    STREAM::encoding utf-8
    STREAM::expression {@استطلاع@شس@}
    STREAM::enable
}

}