[exim] first_delivery condition help

I am using Exim 4.34 and am trying to test some utils we have, I have
tried using the first_delivery condition in a transport_filter line but
it fails expanding

remote_smtp:
transport_filter = ${if first_delivery {...}\
{..}}
results in:

Expansion of "${if" from command "${if first_delivery {/dk/el_dksign -o
/dk/input.txt -l /dk/log.txt}{/dk/el_dksign -d user@???
-o /dk/input.txt -s 2}}" in transport filter failed: condition name
expected, but found ""

It is my understanding that first_delivery can be used in the .conf and
doesnt have to be in a system filter and that it _should_ work. can it
only be used in router sections?


Timothy Der