round robin

Hi, someone can explain me the reason why a got a syntax error with this rules? pass in on $int_if from $int_if:network route-to { ($ext_if $ext_gw) weight 1, ($ext_if2 $ext_gw2) weight 15 } round-robin pass out on $ext_if route-to ($ext_if2 $ext_gw2) from $ext_if2 to any pass out on $ext_if2...